Close 57/64" · Normal 29/32" · Loose 15/16" — nominal + 1/64" / 1/32" / 1/16" to the nearest standard drill (common shop practice).
Hex head (across flats)
1-5/16"
Socket key (across flats)
3/4"
Close 57/64" · Normal 29/32" · Loose 15/16" — nominal + 1/64" / 1/32" / 1/16" to the nearest standard drill (common shop practice).
Tightening torque estimate
Target preload is 75% of proof load; torque is estimated from T = K · F · d.
Grade / class
Stress area
Preload
Torque
SAE Grade 2
0.5205 in²
21472 lbf
313 lb·ft · 3758 lb·in
SAE Grade 5
0.5205 in²
33184 lbf
484 lb·ft · 5807 lb·in
SAE Grade 8
0.5205 in²
46848 lbf
683 lb·ft · 8198 lb·in
These figures assume a nut factor of K = 0.20 (dry / as-received steel). K captures thread and head friction and can swing torque by 30% or more — a lubricated joint needs noticeably less. Change the lubrication assumption in the bolt-torque calculator.
What tap drill do I need for 7/8-16 UN?
For a 7/8-16 UN thread, drill the hole with a 13/16" tap drill (20.64 mm) before tapping. That produces roughly 77% thread engagement, the usual target for a strong, tappable hole. The mating bolt has a major diameter of 22.225 mm and a pitch of 1.588 mm (16 TPI).
To pass a 7/8-16 UN bolt through a part rather than thread it, use a clearance hole: Close 57/64" · Normal 29/32" · Loose 15/16" — nominal + 1/64" / 1/32" / 1/16" to the nearest standard drill (common shop practice)..
All values are generated from the standard thread formulas (ISO 68-1 / ASME B1.1) and published standard tables — not hand-entered. See the full reference.