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Imperial machine screws: #4-40, #6-32, #8-32, 1/4-20

What are the clearance and tap drill sizes for #4-40, #6-32, #8-32 and 1/4-20? · Hardware · basis: ASME B18.6.3 / B18.3; Unified thread standard

sizes
4 in table

Notes

  • Major diameters: #4 2.845 mm (0.112 in), #6 3.505 mm (0.138 in), #8 4.166 mm (0.164 in), 1/4 6.35 mm.
  • Socket head: head dia ≈ 1.5 × major, head height = major. 1/4-20 SHCS: 0.375 in head, 0.25 in tall, 3/16 in hex key.

Sizes

sizemajor_mmtpiclearance_mmtap_drill_mm
#4-402.845403.32.26
#6-323.505323.92.7
#8-324.166324.53.45
1/4-206.35206.85.11

Where the files are

Other publishers' files are linked, not hosted. "verify" = check the license at the link before commercial use.

McMaster-CarrMachine screws (free STEP/IGES/STL per part, for your own design use; no redistribution)STEP, IGES, STL, PDFMcMaster-Carr site terms: personal design use, no redistribution verify
WikipediaUnified Thread StandardwebCC BY-SA 4.0 (text)

Free files

★ Free files 18 parts, generated by Xem Studio from the standard. CC BY 4.0. Threads are plain cylinders at major diameter. index.json

shcs-4-40x6.35mm#4-40 SHCS × 6.35 mm, thread as plain cylinderSTEP · STL
shcs-4-40x9.5mm#4-40 SHCS × 9.5 mm, thread as plain cylinderSTEP · STL
shcs-4-40x12.7mm#4-40 SHCS × 12.7 mm, thread as plain cylinderSTEP · STL
shcs-4-40x19mm#4-40 SHCS × 19 mm, thread as plain cylinderSTEP · STL
shcs-6-32x6.35mm#6-32 SHCS × 6.35 mm, thread as plain cylinderSTEP · STL
shcs-6-32x9.5mm#6-32 SHCS × 9.5 mm, thread as plain cylinderSTEP · STL
shcs-6-32x12.7mm#6-32 SHCS × 12.7 mm, thread as plain cylinderSTEP · STL
shcs-6-32x19mm#6-32 SHCS × 19 mm, thread as plain cylinderSTEP · STL
shcs-6-32x25.4mm#6-32 SHCS × 25.4 mm, thread as plain cylinderSTEP · STL
shcs-8-32x9.5mm#8-32 SHCS × 9.5 mm, thread as plain cylinderSTEP · STL
shcs-8-32x12.7mm#8-32 SHCS × 12.7 mm, thread as plain cylinderSTEP · STL
shcs-8-32x19mm#8-32 SHCS × 19 mm, thread as plain cylinderSTEP · STL
shcs-8-32x25.4mm#8-32 SHCS × 25.4 mm, thread as plain cylinderSTEP · STL
shcs-1-4-20x12.7mm#1-4-20 SHCS × 12.7 mm, thread as plain cylinderSTEP · STL
shcs-1-4-20x19mm#1-4-20 SHCS × 19 mm, thread as plain cylinderSTEP · STL
shcs-1-4-20x25.4mm#1-4-20 SHCS × 25.4 mm, thread as plain cylinderSTEP · STL
shcs-1-4-20x31.75mm#1-4-20 SHCS × 31.75 mm, thread as plain cylinderSTEP · STL
shcs-1-4-20x38.1mm#1-4-20 SHCS × 38.1 mm, thread as plain cylinderSTEP · STL

Plain text: sheet.txt · JSON: /api/geometry?object=imperial-machine-screws

Imperial machine screws: #4-40, #6-32, #8-32, 1/4-20, isometric render of a generated part
Render of shcs-6-32x12.7mm from the free STEP; not to scale.

Fits with

Socket head cap screws, M2–M8 (ISO 4762 / DIN 912), isometric render of a generated part
Socket head cap screws, M2–M8 (ISO 4762 / DIN 912)7 sizes★ 47 files
Schedule 40 pipe and PVC fittings, 1/2 to 2 inch, isometric render of a generated part
Schedule 40 pipe and PVC fittings, 1/2 to 2 inch6 sizes★ 6 files

Questions

What is the diameter of a #4-40, #6-32 and #8-32 screw in mm?

#4-40: 2.845 mm (0.112 in). #6-32: 3.505 mm (0.138 in). #8-32: 4.166 mm (0.164 in). 1/4-20: 6.35 mm.

What is the clearance hole for a #6-32 screw?

3.9 mm (0.1495 in, #25 drill); tap drill 2.7 mm (#36). #4-40: clearance 3.3 mm, tap 2.26 mm (#43). #8-32: clearance 4.5 mm, tap 3.45 mm (#29).

Is #6-32 the same as M3.5?

Close but not interchangeable: #6-32 is 3.505 mm with 32 TPI (0.794 mm pitch); M3.5 is 3.5 mm with a 0.6 mm pitch. Use metric nuts on metric screws.