Close 49/64" · Normal 25/32" · Loose 13/16" — nominal + 1/64" / 1/32" / 1/16" to the nearest standard drill (common shop practice).
Hex head (across flats)
1-1/8"
Socket key (across flats)
5/8"
Close 49/64" · Normal 25/32" · Loose 13/16" — 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
0.3863 in²
15933 lbf
199 lb·ft · 2390 lb·in
SAE Grade 5
0.3863 in²
24624 lbf
308 lb·ft · 3694 lb·in
SAE Grade 8
0.3863 in²
34763 lbf
435 lb·ft · 5215 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 3/4-20 UNEF?
For a 3/4-20 UNEF thread, drill the hole with a 45/64" tap drill (17.86 mm) before tapping. That produces roughly 72% thread engagement, the usual target for a strong, tappable hole. The mating bolt has a major diameter of 19.05 mm and a pitch of 1.27 mm (20 TPI).
To pass a 3/4-20 UNEF bolt through a part rather than thread it, use a clearance hole: Close 49/64" · Normal 25/32" · Loose 13/16" — 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.