Tesco Steel & Engineering forges threadolets — the screwed member of the olet family: an integrally reinforced 90° branch outlet butt-welded to the run pipe, receiving the branch in a female NPT taper thread cut and gauged to ASME B1.20.1. No branch weld at all — the pipe, gauge or valve simply screws in, and comes out the same way: the standard branch for threaded piping systems, pressure-gauge and instrument connections, drains, vents and sample points. Reinforcement is forged into the body per MSS SP-97, in NPS ⅛″ to 6″, Classes 3000 and 6000, reducing and size-on-size, in every material grade on this site: carbon steel, LTCS, the chrome-moly ladder, stainless, duplex and the nickel alloys — BSPT threads against enquiry. Each piece is laser-marked with size, class, grade and heat, threads plug-gauged, certified to EN 10204 3.1/3.2. All three dimension tables in the datasheet below. ISO 9001:2015, made in Mumbai, India — exported to 50+ countries.
MSS SP-97 · NPT to ASME B1.20.1Threaded Outlet · ThredoletNo Branch Weld — Screws InNPS ⅛″–6″ · Class 3000 / 6000Reducing & Size-on-SizeCarbon Steel to Nickel AlloysEN 10204 3.1 / 3.2 · ISO 9001:2015
ASTM A105 Threadolets, 2″ Class 3000, Heat TS4513 — the Female NPT Taper Ready for Make-Up
What is a Threadolet?
The branch that breaks by hand. A threadolet (also written thredolet or threaded outlet) is a forged, integrally reinforced 90° branch outlet fitting: the contoured base is butt-welded to the run pipe, and the branch pipe, gauge or instrument screws into a female NPT taper thread cut to ASME B1.20.1 — no branch weld, no bevel. Reinforcement is forged in per MSS SP-97, so no pad is needed. It is the standard branch for threaded small-bore work: gauges, drains, vents, sample points and threaded piping systems. We forge them NPS ⅛″–6″, Classes 3000 and 6000, reducing and size-on-size, in every grade from A105 to the nickel alloys, threads plug-gauged, laser-marked and certified to EN 10204 3.1/3.2.
Also searched as: threaded outlet, thredolet, NPT outlet, screwed branch fitting, threaded branch connection, MSS SP-97 threaded outlet — all this page's product. Related pages: the weldolet, sockolet and elbolet (all live), the flangeolet, the threaded flanges that share this fitting's thread discipline, and the material pages behind every grade we forge: carbon steel, alloy steel, stainless, duplex, Monel, Inconel and Hastelloy.
Why a Threaded Branch — the Connections That Come Apart
Connection
Why It Threads
Pressure gauges & instruments
Changed out for calibration and replacement — the gauge's own connection is a male taper thread, and the threadolet is its natural seat on the header
Drains & vents
Take plugs and small valves that maintenance removes and refits over the plant's whole life
Sample points
Valves and quills get swapped as the service and the sampling programme change
Temporary connections
Hydrotest points, chemical-cleaning taps, purge lines — installed to be removed
Threaded piping systems
Utility air, water, lube oil, fire water — lines that are threaded end to end need a branch fitting that speaks their language
The run-side weld is the same full-penetration groove weld as a weldolet's; the branch side never sees an arc. That split — welded to the header, screwed to the branch — is the threadolet's whole identity.
MSS SP-97's compensation is in the body profile itself — a code-compliant branch with no reinforcing pad, no field-fabricated compensation, every surface open to inspection.
The Taper Is the Seal
NPT cut and plug-gauged to ASME B1.20.1 — a tapered thread seals by metal-to-metal wedging, so the gauging of the taper, not just the diameter, is what we inspect and record. BSPT to ISO 7-1 against enquiry.
Reducing and Size-on-Size
A smaller branch on a larger run is the classic duty; equal-size outlets are tabulated separately with their bore dimension — both from the same forge, both in the datasheet's tables.
One Fitting, Any Metal
From A105 carbon steel to duplex 2205 and the nickel alloys — and, when a specialised system asks, even aluminium: the outlets photographed below were machined in three sizes for a light-alloy line. The threadolet is a machined forging; the grade is your choice.
Specification Notes — Getting Threadolets Right
Three honest notes.The class-to-schedule mapping is not the socket-weld one: for threaded fittings, Class 3000 corresponds to Schedule 160 pipe and Class 6000 to XXS — one step heavier than the same numbers mean on a sockolet; specify by class and the mapping takes care of itself. The thread lives in the pressure envelope: ASME B31.3 restricts threaded joints under severe cyclic conditions and where vibration works on the joint — on lines like that, seal-weld to the code's rules or move to the welded siblings. And seal welding changes the order: a joint that will be seal-welded is made up clean — no sealant, no PTFE tape — and once welded it no longer breaks by hand; if every joint on the line gets seal-welded, the sockolet was probably the right fitting. State the intent at enquiry.
How Our Threadolets Are Manufactured
1
Material — certified forgings in the ordered grade, heat treated as the grade demands — normalised LF2, N&T chrome-moly, solution-annealed stainless and duplex — furnace records retained; heat-number transfer at the first operation.
2
Body machining — the MSS SP-97 profile turned to the tabulated dimensions for the size and class.
3
Saddle contour — the base machined to the run-pipe curvature stated on the order, ready for the 1.6 mm root-gap fit-up.
4
Thread cutting & gauging — the female NPT taper cut to ASME B1.20.1 and checked with plug gauges — the inspection that is this fitting's signature; BSPT to ISO 7-1 where ordered.
5
Testing & marking — PMI on alloy grades, MPI/DPT/UT to the ordered scope, then laser marking: grade, size, class, heat number.
6
Certification & packing — EN 10204 3.1 MTC (3.2 witnessed on request); threads capped and protected, packed sea-worthy.
Where Threadolets Are Used
Wherever small-bore connections are made and broken: refinery and petrochemical units seat their pressure gauges, sample points and chemical-injection taps on threadolets; power and utility systems branch their threaded air, water and lube-oil lines with them; and skid and package builders use them for every gauge and test point the P&ID scatters across a unit. Production pieces below — the marking on each is real:
Threadolet Dimensions — Class 3000 Quick Reference
A is the height from run-pipe surface to outlet face, B the outside diameter of the base, C the hole to cut in the run pipe; all in millimetres, weights approximate. Set a root gap of about 1.6 mm between base and run pipe before the butt weld.
NPS (inch)
A (mm)
B (mm)
C (mm)
Weight (kg)
⅛
19.05
25.40
15.88
0.05
¼
19.05
25.40
15.88
0.05
⅜
20.64
31.75
19.05
0.09
½
25.40
35.72
23.81
0.11
¾
26.99
43.66
29.37
0.16
1
33.34
50.80
36.51
0.27
1¼
33.34
65.09
44.45
0.41
1½
34.93
72.23
50.80
0.45
2
38.10
88.11
65.09
0.79
2½
46.04
103.19
76.20
1.36
3
50.80
122.24
93.66
1.97
3½
53.98
132.56
101.60
2.61
4
57.15
151.61
120.65
3.22
5
66.68
185.74
141.29
5.44
6
69.85
219.08
169.86
6.94
Two more tables live in the datasheet: Class 6000 reducing outlets in eight sizes from ¼″ to 2″, and size-on-size Class 3000 outlets in twelve sizes from ½″ to 6″ — the equal-size table adding the bore dimension D. Download the datasheet (PDF) for all three, plus the installation guidance — and for stack-ups on a specific header, state run size and schedule, since the installed height rides on the run pipe's curvature as well as A.
How to Specify & Order a Threadolet
Seven elements — the run pipe's size and schedule shape the saddle, so lead with them:
1
Run pipe size and schedule — e.g. 6″ Sch 40; the saddle is contoured to it.
2
Branch size — e.g. 1″ — or size-on-size where run and branch match.
3
Pressure class — 3000 or 6000; for threaded fittings, 3000 maps to Sch 160 pipe and 6000 to XXS.
4
Thread form — NPT to ASME B1.20.1 as standard; BSPT to ISO 7-1 against enquiry.
5
Material grade, exactly — A105, A350 LF2, A182 F316L dual-certified, duplex F51... as your specification writes it.
6
Certification & NDT — EN 10204 3.1 (our standard) / 3.2 witnessed; thread-gauging records, MPI, DPT, UT or NACE scope if extended.
7
Quantity & destination — to sales@tescosteel.com or the inquiry form; say whether the joints will be seal-welded — it travels with the service.
Example: “Threadolet, 1″ branch on 6″ Sch 40 run, Class 3000, NPT per ASME B1.20.1, ASTM A105, B31.3, EN 10204 3.1 — 20 pieces.” Quotations normally within 24 hours with price, unit weights and delivery.
Threadolets — Frequently Asked Questions
What is a threadolet (threaded outlet)?
A threadolet is a forged, integrally reinforced 90° branch outlet fitting that is butt-welded to the run pipe and receives the branch in a female NPT taper thread cut to ASME B1.20.1. It is the screwed member of the olet family: the body and its reinforcement follow MSS SP-97 exactly as a weldolet's do, but the branch pipe, gauge or instrument simply threads in — no branch weld, no bevel, no fillet. That makes it the standard choice for threaded small-bore branches: pressure-gauge and instrument connections, drains, vents and sample points, anywhere the piping practice is threaded or the connection must come apart by hand. We forge threadolets in NPS ⅛" to 6", Classes 3000 and 6000, reducing and size-on-size, in every material grade on this site, each laser-marked and certified to EN 10204 3.1/3.2.
When is a threaded branch the right choice?
When the connection must break by hand. A welded branch is permanent; a threaded one unscrews — and a surprising amount of small-bore work depends on exactly that. Pressure gauges are changed out for calibration; sample points get their valves and quills swapped as the service changes; drains and vents take plugs that maintenance removes and refits; temporary connections — hydrotest points, chemical-cleaning taps, nitrogen purge lines — exist to be removed. Threaded piping systems themselves, common in utility air, water, lube oil and fire-water services, need a branch fitting that speaks their language. The threadolet gives all of these a full-strength, code-reinforced branch on the run pipe while keeping the connection itself a screwed joint. Where the branch will never be broken and the service is severe, the welded siblings — sockolet and weldolet — are the better instinct; the honest limits question below draws that line.
What standards cover threadolets?
Three, dividing the work cleanly. MSS SP-97 — Integrally Reinforced Forged Branch Outlet Fittings — owns the body: the forged-in reinforcement, pressure-temperature basis, marking and material cross-references, exactly as for the rest of the olet family. ASME B1.20.1 owns the thread itself: the NPT taper form, its gauging, and the make-up practice of hand-tight plus one and a half to three turns. ASME B16.11 is the kinship standard — it governs threaded forged fittings generally, so a threadolet's Class 3000 or 6000 rating places it beside the threaded couplings and elbows it serves with; BSPT to ISO 7-1 is cut against enquiry for markets that thread that way. On the line, branch reinforcement logic belongs to the piping code, B31.3 or B31.1 — which is also where the restrictions on threaded joints live. Materials certify to their own standards — A105, A350 LF2, A182, B564 — so the certificate reads like any forging certificate, with the thread gauging recorded alongside.
What sizes and classes do threadolets come in?
Branch sizes run NPS ⅛" through 6" (DN 6 to DN 150) — threaded practice is small-bore practice, and the range reflects it. Two pressure classes: Class 3000, the standard duty, tabulated in fifteen reducing sizes from ⅛" to 6"; and Class 6000 for heavy-wall systems, tabulated from ¼" to 2". One mapping is worth pinning down, because it differs from the socket-weld habit: for threaded fittings per ASME B16.11 practice, Class 3000 corresponds to Schedule 160 pipe and Class 6000 to XXS — one step heavier than the same class numbers mean on a sockolet. A reducing threadolet puts a smaller branch on a larger run; size-on-size outlets, tabulated separately with their bore dimension, put an equal-size branch on the run — our datasheet carries all three tables. As with every olet, each reducing size covers a run range, so one 1" Class 3000 threadolet serves a spread of header sizes; state the actual run size and schedule on the order and the saddle comes contoured to it.
What materials are threadolets available in?
Every grade this site forges — and occasionally one beyond it. Carbon steel A105 is the volume grade, the black-bodied pieces photographed on this page; low-temperature A350 LF2 covers the cold bench; chrome-moly A182 F11, F22, F5, F9 and F91 follow the alloy headers; stainless F304/304L and F316/316L with dual certification where heats qualify, plus stabilised F321 and F347; duplex F51 — the wrapped pieces in the gallery are 2205, laser-marked DN15 3000LB NPT for an export order — and super duplex F53/F55; then the nickel bench: Monel, Inconel, Incoloy, Hastelloy, with copper-nickel and titanium against enquiry. The aluminium threaded outlets photographed here, machined in ¾", ⅜" and ¼" Class 3000 for a specialised light-alloy system, make the wider point: the threadolet is a machined forging, and the works cuts it in whatever certified material the line demands. Chemistry per heat, PMI on alloy grades, EN 10204 3.1/3.2 on every lot.
How is a threadolet installed?
Weld the base, protect the thread, screw in the branch — in that order. The branch location is marked on the run pipe and the opening cut to the datasheet's C dimension; the contoured saddle is fitted with a root gap of roughly 1.6 mm and the base is joined with a full-penetration groove weld, exactly as on a weldolet. The one discipline the threadolet adds is thread care: the female NPT must be protected from weld spatter and heat during the base weld, and on critical work it is re-gauged afterwards, since welding distortion can move a thread that gauged perfectly in the shop. Branch make-up then follows ASME B1.20.1 practice — apply thread sealant or PTFE tape to the male thread, engage hand-tight, and wrench a further one and a half to three turns. No branch welding at all; that is the point of the fitting. Where the code or the service requires it, the made-up joint can be seal-welded — its own question below.
Can a threadolet joint be seal-welded?
Yes — and piping codes commonly require exactly that where threaded joints serve flammable, toxic or higher-severity duty. A seal weld is a small fillet run around the made-up joint, covering the exposed threads; per B31.3 practice it is a leak-tightness measure only and contributes no strength to the joint. Three honest caveats travel with it. First, thread sealant and PTFE tape must be left out of a joint that will be seal-welded — compound trapped under the weld makes porosity, so the joint is made up clean. Second, a seal-welded threadolet has surrendered the threaded joint's whole reason for existing: it no longer breaks by hand, and unmaking it means cutting. Third, if the specification finds itself seal-welding every threaded joint on the line, a sockolet was probably the fitting to order — the same class ratings, a fillet weld that is structural rather than cosmetic, and no thread in the pressure envelope. State seal-welding intent at enquiry and we supply the fitting accordingly.
What are the honest limits of a threaded branch connection?
Three, and stating them plainly is cheaper than discovering them. First, the thread lives in the pressure envelope: a tapered thread is a controlled leak path sealed by metal-to-metal wedging and sealant, and every make-and-break cycle wears it — fine for gauges and drains, wrong for joints broken constantly under severe service. Second, thread roots are stress raisers and the code knows it: ASME B31.3 restricts threaded joints under severe cyclic conditions and steers them away from services where vibration, pressure cycling or bending act on the joint — small threaded branches snapped at the root by pipework vibration are a known failure mode, which is why gussets or a change to socket-weld appear on critical lines. Third, metallurgy: stainless-on-stainless threads gall — anti-seize matters — and crevice-sensitive services dislike the thread's built-in crevice. None of this is a defect of the fitting; it is the physics of any threaded joint. Where the limits bind, the sockolet and weldolet pages on this site describe the welded alternatives.
Threadolet, sockolet or weldolet — which branch fitting do I need?
Ask how the branch will be joined, because the run-side weld is identical on all three — it is the branch end that decides. Threadolet: the branch screws in — for threaded piping systems and for connections that must come apart by hand: gauges, drains, vents, sample points. Sockolet: the branch drops into a B16.11 socket and is fillet-welded — the small-bore workhorse for permanent welded branches to NPS 2, no bevel needed, alignment built in. Weldolet: the branch butt-welds to a bevelled outlet — the full-strength choice at any size, and the only one of the three that runs beyond small-bore, to NPS 24 and above. Class logic differs too: threadolet and sockolet are class-rated 3000/6000 (with the schedule correspondence differing between them — Sch 160/XXS threaded versus Sch 80/160 socket), while the weldolet is schedule-matched to the branch pipe. All three share the MSS SP-97 body and forged-in reinforcement; their pages on this site carry each story in full.
Is 'Threadolet' a brand name?
By origin, yes — and with a spelling worth knowing. The Bonney Forge trademark is Thredolet, without the middle 'a'; the piping trade, writing the word by ear for decades, settled on 'threadolet', and that is the spelling on most requisitions and isometrics today. Both words mean the same fitting, and both long ago became generic in everyday use, exactly as Weldolet and Sockolet did. This page uses the trade spelling in that ordinary generic sense; the descriptive term is threaded outlet or threaded branch outlet fitting. What we manufacture and certify are integrally reinforced forged branch outlet fittings to MSS SP-97 with female NPT threads gauged to ASME B1.20.1 — the wording our certificates carry, dimensionally and functionally interchangeable with any outlet made to the same standards. If your documents write 'thredolet', 'threaded outlet', 'NPT outlet' or 'screwed branch fitting', they mean this product.
What is marked on each threadolet?
Manufacturer, material grade, branch size, class and heat number — laser-marked on the machined body. The production pieces photographed on this page read exactly that way: 'A105 THREADOLET 2" #3000' with heat TS4513 on the large pair, 'A105 THREADOLET 1-1/2" #3000' with heat TS4514 beside them, and the duplex lot marked 'DUPLEX 2205 THREADOLET DN15 3000LB NPT' with heat QT4987 — that last one showing the marking flex to a customer's metric convention, DN15 for ½", on an export order. The heat number is the working end of the marking: it ties each piece to its EN 10204 certificate, its ladle chemistry and its heat-treatment record, and it is what stores check against the certificate before a spool goes to the shop. PMI confirms alloy grades match the mark before dispatch, and project-specific marking — tag numbers, PO references — is applied to order and recorded on the documents.
What testing and certification come with threadolets?
The forging's full paper trail, plus the thread's own check. Chemistry and mechanicals per heat on the EN 10204 3.1 MTC — 3.2 witnessed on request — with heat-treatment condition and furnace records where the grade demands them: normalised LF2, N&T chrome-moly, solution-annealed stainless and duplex. Thread gauging to ASME B1.20.1 with plug gauges is the threadolet's signature inspection — the taper, not just the diameter, is what seals. PMI verifies every alloy piece. NDT to the ordered scope: MPI or DPT of the machined body and thread, UT of the forging where specified, hardness testing for sour service, with NACE MR0175 / ISO 15156 compliance available on request. Dimensional inspection reports to MSS SP-97. Third-party witness or review is routine on project orders; state the agency and scope on the enquiry and the documentation follows the material.
Where can I find threadolet dimensions?
In the datasheet on this page — a three-page PDF with three dimension tables. Class 3000 reducing outlets run fifteen sizes from ⅛" to 6", Class 6000 reducing outlets eight sizes from ¼" to 2", and size-on-size Class 3000 outlets twelve sizes from ½" to 6" — that third table adding the bore dimension D that equal-size outlets need. Each tabulates the height A from run-pipe surface to outlet face, the base outside diameter B, the hole C to be cut in the run pipe, and approximate weight, all in millimetres and kilograms. The Class 3000 table is reproduced on this page for quick reference. Two working notes: the fitting's installed height depends on the run pipe's curvature as well as A, so stack-ups on a specific header should state run size and schedule; and the root gap of about 1.6 mm between saddle and run pipe belongs in the fit-up, not the tables. Non-standard bores, BSPT threads and drawing-specific variants are machined to order.
What details are needed to get an accurate threadolet quotation?
Seven elements plus commercial terms: (1) run pipe size and schedule — the saddle is contoured to it, e.g. 6" Sch 40; (2) branch size — e.g. 1" — or size-on-size where run and branch match; (3) pressure class — 3000 or 6000, remembering the threaded mapping of 3000 to Sch 160 and 6000 to XXS; (4) thread form — NPT to ASME B1.20.1 as standard, BSPT to ISO 7-1 against enquiry; (5) material grade, exactly as your specification writes it — A105, A350 LF2, A182 F316L, duplex F51; (6) certification and NDT — EN 10204 3.1 (our standard) or 3.2 witnessed, thread gauging records, plus MPI/DPT/UT or NACE scope where extended; (7) quantity and destination — and whether the joints will be seal-welded, which travels with the service. Send it to sales@tescosteel.com or through the inquiry form; quotations normally return within 24 hours with price, unit weights and delivery, and common A105 and stainless combinations usually quote from stock.
Who manufactures threadolets in India?
Tesco Steel & Engineering is an ISO 9001:2015 certified manufacturer based in Mumbai, India, forging integrally reinforced branch outlet fittings to MSS SP-97 with female NPT threads gauged to ASME B1.20.1 — threadolets (threaded outlets) in NPS ⅛" to 6", Classes 3000 and 6000, reducing and size-on-size. Materials span our whole forge: carbon steel A105, LTCS A350 LF2, chrome-moly A182 F11 through F91, stainless 304/316/321/347 families, duplex 2205 and super duplex, the nickel alloys — and specialised materials like the aluminium outlets photographed on this page, machined against enquiry. PMI verification, laser marking tying each piece to its heat, and EN 10204 3.1/3.2 certification on every lot. The same works supplies the complete olet family — weldolets, sockolets, elbolets, nipolets, latrolets, sweepolets and flangeolets — alongside the flange ranges this site is built around. Exported to more than 50 countries; datasheet with all three dimension tables downloadable on this page.
