Dimensions, drill sizes and wrench sizes for 1-1/8-12 UNF.
Designation
1-1/8-12 UNF
Major (outside) diameter
28.575 mm · 1.125"
Pitch
2.117 mm · 12 TPI
Pitch diameter
27.2 mm · 1.0709"
Minor diameter (external)
25.978 mm · 1.0228"
Minor diameter (internal)
26.284 mm · 1.0348"
Recommended tap drill
1-3/64" · 26.59 mm · ≈72% thread
Clearance hole
Close 1-9/64" · Normal 1-5/32" · Loose 1-3/16" - nominal + 1/64" / 1/32" / 1/16" (common shop practice), given as the sums themselves because they are larger than the 1" end of the standard drill table.
Hex head (across flats)
1-11/16"
Close 1-9/64" · Normal 1-5/32" · Loose 1-3/16" - nominal + 1/64" / 1/32" / 1/16" (common shop practice), given as the sums themselves because they are larger than the 1" end of the standard drill table.
1-1/8-12 UNF in numbers
1-1/8-12 UNF is 1.1250 in across the crests with 12 threads per inch, a 2.117 mm pitch. The basic pitch diameter is 27.2 mm and the bolt's minor diameter 25.978 mm, so the thread is 1.298 mm deep on the bolt. Its tensile stress area is 0.8557 in², 12% more than the coarser 1-1/8-7 UNC at the same diameter. A class 2A bolt is made with its pitch diameter between 1.0631 and 1.0691 in, and a class 2B nut between 1.0709 and 1.0787 in, so even the largest bolt clears the smallest nut by 0.0018 in. The nearest metric size, M30 × 3.5, is 1.43 mm larger across the crests and its pitch is 1.383 mm coarser, so the two do not interchange.
Tap drill by thread percentage
Hole = D − % × 0.0129904 × P, with D = 28.575 mm and P = 2.117 mm. A smaller hole leaves more thread; the recommended 1-3/64" drill above gives about 72%.
Tap-drill hole diameters for 1-1/8-12 UNF at several thread percentages.
Thread
Hole (mm)
Hole (in)
60%
26.92
1.0600
65%
26.79
1.0546
70%
26.65
1.0492
75%
26.51
1.0438
Class 2A and 2B limits
The commercial fit for 1-1/8-12 UNF: class 2A for the bolt, class 2B for the nut or tapped hole. Inches.
Class 2A external and class 2B internal limits of size for 1-1/8-12 UNF.
Dimension
Min
Max
2A major diameter
1.1118
1.1232
2A pitch diameter
1.0631
1.0691
2B pitch diameter
1.0709
1.0787
Matches the ASME B1.1 class 2A/2B table for this size, as printed in the data sheets of American Fastener (Cap Screws & Bolts - External Threads Class 2A) and American Fastener (Nuts - Internal Threads - Class 2B). Basic pitch diameter E = D − 0.649519 P = 1.0709; the allowance between basic and the 2A limits is 0.0018. The B1.1 formula, class 2A pitch tolerance T = 0.0015 D^(1/3) + 0.0015 √D + 0.015 P^(2/3) with the allowance 0.3 T and the 2B tolerance 1.3 T, gives the same figures for this size. Minor-diameter limits are not given here.
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 1-1/8-12 UNF by fastener grade or property class.
Grade / class
Stress area
Preload
Torque
SAE Grade 2
0.8557 in²
21179 lbf
397 lb·ft · 4765 lb·in
SAE Grade 5
0.8557 in²
47493 lbf
890 lb·ft · 10686 lb·in
SAE Grade 8
0.8557 in²
77015 lbf
1444 lb·ft · 17328 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.
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 1-1/8-12 UNF 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 1-1/8-12 UNF thread, drill the hole with a 1-3/64" tap drill (26.59 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 28.575 mm and a pitch of 2.117 mm (12 TPI).
To pass a 1-1/8-12 UNF bolt through a part rather than thread it, use a clearance hole: Close 1-9/64" · Normal 1-5/32" · Loose 1-3/16" - nominal + 1/64" / 1/32" / 1/16" (common shop practice), given as the sums themselves because they are larger than the 1" end of the standard drill table..
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 1-1/8-12 UNF thread?
Drill 1-3/64" (26.59 mm) before tapping 1-1/8-12 UNF. That leaves roughly 72% thread engagement, the usual target for a strong hole that still taps cleanly.
Is 1-1/8-12 UNF a coarse or fine thread?
1-1/8-12 UNF is a Unified fine (UNF) thread at 12 threads per inch. Fine pitches have a larger stress area than coarse at the same diameter and suit thin walls, fine adjustment and vibration-sensitive joints.
What size clearance hole does a 1-1/8-12 UNF bolt need?
Close 1-9/64" · Normal 1-5/32" · Loose 1-3/16" - nominal + 1/64" / 1/32" / 1/16" (common shop practice), given as the sums themselves because they are larger than the 1" end of the standard drill table. A clearance hole lets the 1-1/8-12 UNF bolt pass through the part instead of threading into it.
How much torque should I use on a 1-1/8-12 UNF bolt?
Estimated tightening torque for 1-1/8-12 UNF runs from 397 lb·ft (SAE Grade 2) to 1444 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.