Customisation scope for thread length variants

Externally threaded studs (M1/SM1)

Thread length (L) can be customised in 1 mm increments, within these ranges according to thread size:

• M4: 5 – 40 mm
• M5: 5 – 60 mm
• M6: 10 – 100 mm
• M8: 12 – 100 mm
• M10: 20 – 100 mm

Shoulder geometry remains the same as the equivalent standard stud.

Compatible thread sizes by Head type:

• B15: M4 – M6
• B20, B23: M4 – M8
• B30, B32, B38A, T38A: M4 – M10

Internally threaded collars (F2/SF2)

Collar lengths can be customised in 1 mm increments, within these ranges according to thread size:

• M4 – M10: 5 – 40 mm
• M12: 10 – 40 mm

All other collar geometry remains standard.

Compatible thread sizes by Head type:

Blind Heads (screw does not pass through):

• B20, B23, T38A: M4 – M8
• B30, B32, B38A: M4 – M12

Sighted Heads (screw passes through):

• S20, S23, ST38A: M4 – M8
• S30, S32, S38A: M4 – M12

What's outside the scope of thread length customisation

Some requests are out-of-scope due to manufacturing constraints. Examples:

• Thread lengths outside the minimum and maximum values
• Changes to collar and Head geometry
• Combining thread length variants with other customisations (e.g. alternative finishes)

If you have an out-of-scope request, we can work with you to create a solution – get in touch.

Design and performance considerations for thread length variants

Thread‑length customisation affects only the threaded element of the stud or collar. All other geometry, and therefore all loadability characteristics, remain unchanged.

The main design considerations relate to overall product length, screw engagement, and screw clearance requirements.

Externally threaded studs (M1/SM1)

Custom thread length (L) determines the majority of the overall product length. Two additional dimensions also contribute:

• Shoulder height (L1):
  • M4 – M6 → 1.2 mm
  • M8 – M10 → 1.5 mm
• Head thickness (T): 1.2 mm

Overall length formula: Total length = L + L1 + T

Examples

Minimum overall lengths:

• M4 and M5 = 7.4 mm (5 + 1.2 + 1.2)
• M6 = 12.4 mm (10 + 1.2 + 1.2)
• M8 = 14.7 mm (12 + 1.5 + 1.2)
• M10 = 22.7 mm (20 + 1.5 + 1.2)

Maximum overall lengths:

• M4 = 42.4 mm (40 + 1.2 + 1.2)
• M5 = 62.4 mm (60 + 1.2 + 1.2)
• M6 = 102.4 mm (100 + 1.2 + 1.2)
• M8 and M10 = 102.7 mm (100 + 1.5 + 1.2)

These calculations confirm the overall stud length, on which you can base the necessary clearances to prevent clashes with nearby components during assembly or with mould tooling during co‑processing.

Internally threaded collars (F2/SF2)

For collars, the custom length (L) determines both:

• Overall product length, and
• Maximum screw engagement (with different rules for blind vs sighted Heads)

Overall length formula: Total = L + head thickness (1.2 mm)

Examples:

• M4 – M10 minimum: 6.2 mm
• M12 minimum: 11.2 mm
• All sizes maximum: 41.2 mm

Blind Heads – screw tip clearance

Blind collars require a clearance allowance (Lu) to prevent the screw tip from bottoming out, which can cause deformation and irreparable damage:

• M4: 1.4 mm
• M5: 1.6 mm
• M6: 2 mm
• M8: 2.5 mm
• M10: 3 mm
• M12: 3.5 mm

Usable thread length: Le=L-Lu

This value determines the maximum screw thread acceptance for blind Head collars.

Sighted Heads – screw engagement

For sighted collars, the screw passes through the Head. Therefore:

• Maximum screw engagement ≈ collar length (L)
• No clearance deduction is required

For help, see our guide to screw length selection, or get in touch.

Specification examples for thread length customisation

Example 1: Carbon steel, bright zinc plate (BZP) finish

To specify an externally threaded stud, M5 × 50 mm, on a B20 Head:

• Product type: M1/B20
• Thread diameter: M5
• Customised thread length (L): 50 mm
• Stud material suffix: HT (carbon steel, heat treated)

→ M1/B20 M5 × 50 HT

Example 2: 316 stainless steel

To specify an internally threaded collar, M8 × 32 mm, on a sighted S38A Head:

• Material prefix: S (316 stainless steel)
• Product type: F2/S38A
• Thread diameter: M8
• Customised collar length (L): 32 mm

→ SF2/S38A M8 × 32

Example 3: Out of scope

A request for M10 × 50 mm collar on a blind T38A head is not possible through our customisation service. 50 mm exceeds the 40 mm maximum collar length and M10 thread size is outside the T38A Head compatibility scope.

Instead, we can create a solution for you through our Create service.