Dimensions, drill sizes and wrench sizes for 5/8-16 UN.
Designation
5/8-16 UN
Major (outside) diameter
15.875 mm · 0.625"
Pitch
1.588 mm · 16 TPI
Pitch diameter
14.844 mm · 0.5844"
Minor diameter (external)
13.927 mm · 0.5483"
Minor diameter (internal)
14.157 mm · 0.5573"
Recommended tap drill
9/16" · 14.29 mm · ≈77% thread
Clearance hole
Close 41/64" · Normal 21/32" · Loose 11/16" - nominal + 1/64" / 1/32" / 1/16" to the nearest standard drill (common shop practice).
Hex head (across flats)
15/16"
Socket key (across flats)
1/2"
Close 41/64" · Normal 21/32" · Loose 11/16" - 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.
Proof-load preload and estimated tightening torque for 5/8-16 UN by fastener grade or property class.
Grade / class
Stress area
Preload
Torque
SAE Grade 2
0.2499 in²
10309 lbf
107 lb·ft · 1289 lb·in
SAE Grade 5
0.2499 in²
15933 lbf
166 lb·ft · 1992 lb·in
SAE Grade 8
0.2499 in²
22493 lbf
234 lb·ft · 2812 lb·in
Strengths are SAE J429 for this diameter band. J429 steps down with size: Grade 2 falls to 33 ksi proof above 3/4 in and Grade 5 to 74 ksi above 1 in, so these figures are not the small-size values. The Grade 2 row applies to bolts up to 6 in long; a longer Grade 2 bolt of the same diameter drops to 33 ksi proof.
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.
Put 5/8-16 UN on a job sheet
The bolt schedule collects the fasteners for one job onto a single sheet - tap drill, wrench size, grade and tightening torque on every line, taken straight from pages like this one. Free schedules hold 3 lines and are saved in this browser only.
For a 5/8-16 UN thread, drill the hole with a 9/16" tap drill (14.29 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 15.875 mm and a pitch of 1.588 mm (16 TPI).
To pass a 5/8-16 UN bolt through a part rather than thread it, use a clearance hole: Close 41/64" · Normal 21/32" · Loose 11/16" - 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.
Frequently asked questions
What drill size do I need to tap a 5/8-16 UN thread?
Drill 9/16" (14.29 mm) before tapping 5/8-16 UN. That leaves roughly 77% thread engagement, the usual target for a strong hole that still taps cleanly.
Is 5/8-16 UN a coarse or fine thread?
5/8-16 UN is in the UN constant-pitch series: it runs 16 threads per inch, a pitch shared across a range of diameters rather than scaled with the size.
What size clearance hole does a 5/8-16 UN bolt need?
Close 41/64" · Normal 21/32" · Loose 11/16" - nominal + 1/64" / 1/32" / 1/16" to the nearest standard drill (common shop practice). A clearance hole lets the 5/8-16 UN bolt pass through the part instead of threading into it.
How much torque should I use on a 5/8-16 UN bolt?
Estimated tightening torque for 5/8-16 UN runs from 107 lb·ft (SAE Grade 2) to 234 lb·ft (SAE Grade 8), targeting 75% of proof load with a dry nut factor of K = 0.20. Lubricated threads need noticeably less torque.
Nearest standard metric sizes by major diameter. These are substitutes by size only - the thread forms are not interchangeable, so never run one into the other.