Dimensions, drill sizes and wrench sizes for 9/16-20 UN.
Designation
9/16-20 UN
Major (outside) diameter
14.288 mm · 0.5625"
Pitch
1.27 mm · 20 TPI
Pitch diameter
13.463 mm · 0.53"
Minor diameter (external)
12.729 mm · 0.5012"
Minor diameter (internal)
12.913 mm · 0.5084"
Recommended tap drill
33/64" · 13.1 mm · ≈72% thread
Clearance hole
Close 37/64" · Normal 19/32" · Loose 5/8" - nominal + 1/64" / 1/32" / 1/16" to the nearest standard drill (common shop practice).
Hex head (across flats)
13/16"
Close 37/64" · Normal 19/32" · Loose 5/8" - 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 9/16-20 UN by fastener grade or property class.
Grade / class
Stress area
Preload
Torque
SAE Grade 2
0.2073 in²
8552 lbf
80 lb·ft · 962 lb·in
SAE Grade 5
0.2073 in²
13217 lbf
124 lb·ft · 1487 lb·in
SAE Grade 8
0.2073 in²
18659 lbf
175 lb·ft · 2099 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 9/16-20 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 9/16-20 UN thread, drill the hole with a 33/64" tap drill (13.1 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 14.288 mm and a pitch of 1.27 mm (20 TPI).
To pass a 9/16-20 UN bolt through a part rather than thread it, use a clearance hole: Close 37/64" · Normal 19/32" · Loose 5/8" - 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 9/16-20 UN thread?
Drill 33/64" (13.1 mm) before tapping 9/16-20 UN. That leaves roughly 72% thread engagement, the usual target for a strong hole that still taps cleanly.
Is 9/16-20 UN a coarse or fine thread?
9/16-20 UN is in the UN constant-pitch series: it runs 20 threads per inch, a pitch shared across a range of diameters rather than scaled with the size.
What size clearance hole does a 9/16-20 UN bolt need?
Close 37/64" · Normal 19/32" · Loose 5/8" - nominal + 1/64" / 1/32" / 1/16" to the nearest standard drill (common shop practice). A clearance hole lets the 9/16-20 UN bolt pass through the part instead of threading into it.
How much torque should I use on a 9/16-20 UN bolt?
Estimated tightening torque for 9/16-20 UN runs from 80 lb·ft (SAE Grade 2) to 175 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.