Double End Studs (Double Ended Studs / Tap End Studs)
In engines, manifolds, gearboxes, and heavy machinery housings, the joint often fails before the fastener breaks—typically due to stripped base threads, preload loss after thermal cycling, or repeated maintenance damaging the tapped hole. Double end studs solve a practical engineering problem: keep the “wear” on a replaceable nut side, and protect the parent material by controlling the embedment (tap end) length. When specified to DIN 938 / DIN 939 / DIN 835 or IFI 136, and matched to the right grade (e.g., 8.8 / 10.9 or ASTM A193 B7), a stud joint becomes more repeatable in torque-to-preload behaviour and more serviceable over the equipment’s life.
- Protect tapped base threads
- Improve repeatable preload build
- Reduce galling with coatings
- Support unequal thread lengths
- Enable quick field replacement
- Provide DIN/ASTM traceability
Technical Specifications
Product Name
Double End Studs / Double Ended Studs (with shank)
Standards
DIN 938 (tap end ≈ 1d), DIN 939 (tap end ≈ 1.25d), DIN 835 (tap end ≈ 2d), IFI 136 (inch), ASTM A193 B7 studs
Material
Carbon steel (C35/C45), alloy steel (e.g., 42CrMo4), stainless steel (A2/304, A4/316)
Grades
ISO 898-1 (e.g., 8.8 / 10.9), stainless per ISO 3506 (A2-70 / A4-70 / A4-80), ASTM A193 B7
Diameter Range
Metric: M6–M36 (typical); Inch: 1/4″–1-1/2″ (typical)
Surface Finish
Plain, Zinc plated, Yellow zinc, Black oxide, Phosphate, HDG (by requirement)
Certifications
ISO 9001; EN 10204 3.1 on request; RoHS/REACH on request; PPAP/IATF capability on request
Stripped base threads during maintenance
What happens: In aluminium housings or cast iron flanges, repeated nut removal + re-torque can damage the tapped hole, especially when the installer “chases” torque after gasket relaxation. Once the base thread is compromised, the repair cost is high (helicoil / oversize tap / replacement part).
Stud solution: A tap end stud keeps the base interface stable. You can specify the embedment length per DIN 938/939/835 (1d / 1.25d / 2d concept) to suit parent material strength and temperature cycling.
Preload loss under thermal cycling (manifold studs / exhaust studs)
What happens: Hot-cold cycles relax gaskets and embed coatings; preload decays, nuts loosen, and micro-sliding accelerates fretting and leakage.
Stud solution: Use high-temperature capable material sets (e.g., ASTM A193 B7 studs with suitable nuts) and control lubrication/finish to stabilise torque scatter. Consider prevailing-torque locking on the nut side where vibration is present.
Misalignment during assembly
What happens: Bolts can “pull” the joint into alignment while damaging threads; studs guide the mating component, improving positional repeatability in flanges and housings.
Stud solution: Select stud bolts with shank (smooth centre) for shear transfer and positioning, instead of relying on threads in the shear plane.
Galling on stainless
What happens: Stainless-on-stainless (304/316) can seize during tightening.
Stud solution: Specify stainless grade per ISO 3506 and apply anti-seize; avoid dry assembly and verify nut material/finish compatibility.
For double end studs, drawing checks focus on d, pitch P, overall length L, tap end thread length l1, nut end thread length l2, and shank length ls (if applicable). (Across flats s applies to nuts, not studs.)
Example Metric Coarse Sizes (common selection):
| Thread Size (d) | Pitch P | DIN Reference (tap end concept) | Tap End Thread Length l1 (rule-of-thumb) | Nut End Thread Length l2 (typical) | Overall Length L (example) | Shank Length ls (example) |
|---|---|---|---|---|---|---|
| M8 | 1.25 | DIN 938 / 939 | 1d–1.25d | 20–30 mm | 60 mm | 15–25 mm |
| M10 | 1.5 | DIN 938 / 939 | 1d–1.25d | 25–35 mm | 80 mm | 20–35 mm |
| M12 | 1.75 | DIN 938 / 939 / 835 | 1d–2d | 30–45 mm | 100 mm | 25–45 mm |
| M16 | 2.0 | DIN 939 / 835 | 1.25d–2d | 35–55 mm | 120 mm | 30–55 mm |
Notes for SEO + procurement:
Search behaviour often includes “M10 double end stud dimensions”, “DIN 938 M12”, “DIN 939 stud”, or “ASTM A193 B7 stud length”.
If the stud is unequal length, specify l1/l2 clearly (tap end vs nut end).
If the application is shear-sensitive, request reduced shank or controlled shank diameter only when the design demands it—otherwise standard shank is preferred for interchangeability.
Key terms covered: Torque, Preload, Lubrication, Washers, Hole Clearance (ISO 273)
Base thread preparation (tap end studs)
Verify thread class and cleanliness; contamination increases friction and produces false torque.
For soft parent materials (aluminium), embedment length selection matters: 1d may be insufficient for high preload; consider 1.25d–2d (aligned with DIN 939 / DIN 835 concepts) based on design requirements.
Stud installation method (prevent bottoming & thread damage)
Avoid bottoming the stud in blind holes—bottoming creates high local stress and unreliable preload.
Use double-nut driving only when necessary; for controlled assembly, specify an installation torque or turn-of-nut method for the tap end if the design requires it.
Torque–Preload control (nut side)
Torque alone is not preload; friction dominates scatter.
Lubrication:
Stainless studs: use anti-seize to reduce galling and torque spikes.
High-strength alloy studs: control lubrication to avoid over-preload.
If preload is critical, validate with torque–tension testing (e.g., aligned with ISO 16047) rather than generic charts.
Washer strategy (bearing stress & embedment)
Use flat washers under the nut to distribute load and reduce embedment-related preload loss.
For coated surfaces or slots, increase washer OD or use load-spreading plates.
Hole clearance for the passing component (ISO 273)
For the flange/plate that passes over the studs, apply clearance holes per ISO 273 to prevent side-loading and bending.
Misalignment forces the stud into bending fatigue; correct the hole pattern or fixture, not the fastener.
Locking in vibration / thermal cycling
Exhaust/manifold service: consider prevailing-torque all-metal lock nuts rather than nylon inserts (nylon softens with temperature).
For critical joints, use a defined locking strategy (prevailing torque, jam nuts, or mechanical locking) and document it in the work instruction.
Related Products
FAQ
What is a double end stud used for?
A double end stud is used to fasten parts to a tapped base material while keeping the replaceable nut side as the wear interface. This improves serviceability and helps protect parent threads in engines, manifolds, housings, and machinery frames.
What is the difference between DIN 938 and DIN 939 studs?
DIN 938 and DIN 939 mainly differ by the tap end (screw-in) length ratio. DIN 938 is commonly associated with a shorter screw-in length (≈1d concept), while DIN 939 uses a longer screw-in length (≈1.25d concept), supporting higher pull-out resistance in the base material.
When should I specify ASTM A193 B7 studs?
Specify ASTM A193 B7 studs when you need high-strength alloy steel performance for higher temperature or pressure bolting sets. They are common in petrochemical, piping flange, and heavy industrial maintenance applications.
Why do studs loosen in exhaust or manifold joints?
Studs loosen mainly due to preload loss from thermal cycling and joint embedment rather than the stud “failing”. Selecting suitable materials/grades, using appropriate locking nuts, and controlling lubrication/torque helps stabilise preload through heat cycles.
How do I prevent thread stripping in the base material with tap end studs?
Prevent stripping by selecting adequate embedment length (often 1.25d–2d for weaker materials), ensuring correct thread class and clean tapped holes, and avoiding bottoming in blind holes. If preload is high, confirm pull-out capacity with the parent material specification and joint design assumptions.