Unified Thread Atlas
Flagship engineering explorer for thread designations across Metric, UNC, and UNF systems.
Search metric, UNC, and UNF thread designations in one engineering explorer.
Each result includes pitch, tap drill, clearance holes, hex size, standards context, and tool links.
Use one search and filter system instead of switching between separate atlases.
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1/4-20 UNC
UNC · 0.25 in · 20 TPI
Tap drill: 0.201 in
Clearance hole: 0.257/0.266/0.281 in
Hex size: 0.438 in
Related standards: ASME B1 1, ISO 261, ISO 262
Equivalent metric: M6x1
Tools: thread identifier · thread pitch to tpi converter · tap drill calculator
1/4-28 UNF
UNF · 0.25 in · 28 TPI
Tap drill: 0.213 in
Clearance hole: 0.257/0.266/0.281 in
Hex size: 0.438 in
Related standards: ASME B1 1, ISO 261, ISO 262
Equivalent metric: M6x1
Tools: thread identifier · thread pitch to tpi converter · tap drill calculator
3/8-16 UNC
UNC · 0.375 in · 16 TPI
Tap drill: 0.3125 in
Clearance hole: 0.386/0.397/0.413 in
Hex size: 0.563 in
Related standards: ASME B1 1, ISO 261, ISO 262
Equivalent metric: M10x1.5
Tools: thread identifier · thread pitch to tpi converter · tap drill calculator
3/8-24 UNF
UNF · 0.375 in · 24 TPI
Tap drill: 0.332 in
Clearance hole: 0.386/0.397/0.413 in
Hex size: 0.563 in
Related standards: ASME B1 1, ISO 261, ISO 262
Equivalent metric: M10x1.5
Tools: thread identifier · thread pitch to tpi converter · tap drill calculator
5/16-18 UNC
UNC · 0.313 in · 18 TPI
Tap drill: 0.257 in
Clearance hole: 0.323/0.332/0.348 in
Hex size: 0.5 in
Related standards: ASME B1 1, ISO 261, ISO 262
Equivalent metric: M8x1.25
Tools: thread identifier · thread pitch to tpi converter · tap drill calculator
5/16-24 UNF
UNF · 0.313 in · 24 TPI
Tap drill: 0.272 in
Clearance hole: 0.323/0.332/0.348 in
Hex size: 0.5 in
Related standards: ASME B1 1, ISO 261, ISO 262
Equivalent metric: M8x1.25
Tools: thread identifier · thread pitch to tpi converter · tap drill calculator
M10
Metric · 10 mm · 1.5 mm
Tap drill: 8.5 mm
Clearance hole: 10.5/11/12 mm
Hex size: 17 mm
Related standards: ISO 261, ISO 262, ISO 724, ISO 965 1
Equivalent metric: M10
Tools: thread identifier · thread pitch to tpi converter · tap drill calculator
M10
Metric · 10 mm · 1.25 mm
Tap drill: 8.8 mm
Clearance hole: 10.5/11/12 mm
Hex size: 17 mm
Related standards: ISO 261, ISO 262, ISO 724, ISO 965 1
Equivalent metric: M10
Tools: thread identifier · thread pitch to tpi converter · tap drill calculator
M12
Metric · 12 mm · 1.75 mm
Tap drill: 10.2 mm
Clearance hole: 13/13.5/14.5 mm
Hex size: 19 mm
Related standards: ISO 261, ISO 262, ISO 724, ISO 965 1
Equivalent metric: M12
Tools: thread identifier · thread pitch to tpi converter · tap drill calculator
M12
Metric · 12 mm · 1.25 mm
Tap drill: 10.8 mm
Clearance hole: 13/13.5/14.5 mm
Hex size: 19 mm
Related standards: ISO 261, ISO 262, ISO 724, ISO 965 1
Equivalent metric: M12
Tools: thread identifier · thread pitch to tpi converter · tap drill calculator
M16
Metric · 16 mm · 2 mm
Tap drill: 14 mm
Clearance hole: 17/18/20 mm
Hex size: 24 mm
Related standards: ISO 261, ISO 262, ISO 724, ISO 965 1
Equivalent metric: M16
Tools: thread identifier · thread pitch to tpi converter · tap drill calculator
M16
Metric · 16 mm · 1.5 mm
Tap drill: 14.5 mm
Clearance hole: 17/18/20 mm
Hex size: 24 mm
Related standards: ISO 261, ISO 262, ISO 724, ISO 965 1
Equivalent metric: M16
Tools: thread identifier · thread pitch to tpi converter · tap drill calculator
M20
Metric · 20 mm · 2.5 mm
Tap drill: 17.5 mm
Clearance hole: 21/22/24 mm
Hex size: 30 mm
Related standards: ISO 261, ISO 262, ISO 724, ISO 965 1
Equivalent metric: M20
Tools: thread identifier · thread pitch to tpi converter · tap drill calculator
M20
Metric · 20 mm · 2 mm
Tap drill: 18 mm
Clearance hole: 21/22/24 mm
Hex size: 30 mm
Related standards: ISO 261, ISO 262, ISO 724, ISO 965 1
Equivalent metric: M20
Tools: thread identifier · thread pitch to tpi converter · tap drill calculator
M3
Metric · 3 mm · 0.5 mm
Tap drill: 2.5 mm
Clearance hole: 3.2/3.4/3.6 mm
Hex size: 5.5 mm
Related standards: ISO 261, ISO 262, ISO 724, ISO 965 1
Equivalent metric: M3
Tools: thread identifier · thread pitch to tpi converter · tap drill calculator
M4
Metric · 4 mm · 0.7 mm
Tap drill: 3.3 mm
Clearance hole: 4.3/4.5/4.8 mm
Hex size: 7 mm
Related standards: ISO 261, ISO 262, ISO 724, ISO 965 1
Equivalent metric: M4
Tools: thread identifier · thread pitch to tpi converter · tap drill calculator
M5
Metric · 5 mm · 0.8 mm
Tap drill: 4.2 mm
Clearance hole: 5.3/5.5/5.8 mm
Hex size: 8 mm
Related standards: ISO 261, ISO 262, ISO 724, ISO 965 1
Equivalent metric: M5
Tools: thread identifier · thread pitch to tpi converter · tap drill calculator
M6
Metric · 6 mm · 1 mm
Tap drill: 5 mm
Clearance hole: 6.4/6.6/7 mm
Hex size: 10 mm
Related standards: ISO 261, ISO 262, ISO 724, ISO 965 1
Equivalent metric: M6
Tools: thread identifier · thread pitch to tpi converter · tap drill calculator
M8
Metric · 8 mm · 1.25 mm
Tap drill: 6.8 mm
Clearance hole: 8.4/9/10 mm
Hex size: 13 mm
Related standards: ISO 261, ISO 262, ISO 724, ISO 965 1
Equivalent metric: M8
Tools: thread identifier · thread pitch to tpi converter · tap drill calculator
M8
Metric · 8 mm · 1 mm
Tap drill: 7 mm
Clearance hole: 8.4/9/10 mm
Hex size: 13 mm
Related standards: ISO 261, ISO 262, ISO 724, ISO 965 1
Equivalent metric: M8
Tools: thread identifier · thread pitch to tpi converter · tap drill calculator