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).
9/16-20 UN in numbers
9/16-20 UN is 0.5625 in across the crests with 20 threads per inch, a 1.27 mm pitch. The basic pitch diameter is 13.463 mm and the bolt's minor diameter 12.729 mm, so the thread is 0.78 mm deep on the bolt. Its tensile stress area is 0.2073 in², 14% more than the coarser 9/16-12 UNC at the same diameter. The nearest metric size, M14 × 2.0, is 0.29 mm smaller across the crests and its pitch is 0.730 mm coarser, so the two do not interchange.
Tap drill by thread percentage
Hole = D − % × 0.0129904 × P, with D = 14.288 mm and P = 1.27 mm. A smaller hole leaves more thread; the recommended 33/64" drill above gives about 72%.
Tap-drill hole diameters for 9/16-20 UN at several thread percentages.
Thread
Hole (mm)
Hole (in)
Nearest drill
60%
13.30
0.5235
no standard drill within 1/64 in
65%
13.22
0.5203
33/64" (0.5156 in) gives 72%
70%
13.13
0.5171
33/64" (0.5156 in) gives 72%
75%
13.05
0.5138
33/64" (0.5156 in) gives 72%
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 come from the standard thread formulas (ISO 68-1 / ASME B1.1) and published standard tables. 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.