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CoilThread Screw Locking Inserts

KATO screw locking inserts exert a prevailing torque on male threaded fasteners to prevent loosening due to vibration or impact. Locking inserts eliminate the need for less desirable and costly locking mechanisms. They are excellent in adjusting screw applications by preventing the male fastener from creeping.

How CoilThread Screw Locking Inserts Work:

KATO

One of the biggest misconceptions regarding locking type helical coil screw thread inserts is the insert has a feature that locks it into place in the parent material. This is not the case. Locking inserts apply a locking, or prevailing, torque on the male fastener.

Locking inserts contain one or more coils that have a series of straight segments. Upon entry of the bolt these straight segments are flexed outwardly, creating pressure on the bolt. This pressure is applied between the flanks of the bolt thread so that contact area is maximized.

CoilThread screw locking inserts are manufactured to meet the locking torque requirment specified in NASM8846. NASM8846 requires the inserts to pass a 15 cycle torque test; it is often possible to realize cycle life far in excess of specification requirements.

For additional information on locking inserts and prevailing torque, please read these articles in KATOpedia:

Location of Locking Coil(s):

  • For 1, 1-1/2 and 2 diameter lengths: The center of the locking coil(s) equals 1/2 the number of free coils.
  • For 2-1/2 and 3 diameter lengths: The locking coil is located the same distance as the 2 diameter length inserts.

Locking Torque

Unified Locking CoilThread (Tangless and Tanged) inserts produce torque values in accordance with NASM8846 when tested with heat treated cadmium-plated bolts. Metric Locking CoilThread (Tangless and Tanged) inserts produce torque values in accordance with MA1565 when tested with heat treated cadmium-plated bolts.

Unified Thread Sizes

Thread
Size
Maximum Locking
Torque
Minimum Breakaway
Torque
Unified Coarse
2-56 20.0 oz-in 3.0 oz-in
3-48 32.0 oz-in 7.0 oz-in
4-40 48.0 oz-in 10.0 oz-in
5-40 75.2 oz-in 13.0 oz-in
6-32 6.0 lbf-in 1.0 lbf-in
8-32 9.0 lbf-in 1.5 lbf-in
10-24 13.0 lbf-in 2.0 lbf-in
12-241 24.0 lbf-in 3.0 lbf-in
1/4-20 30.0 lbf-in 4.5 lbf-in
5/16-18 60.0 lbf-in 7.5 lbf-in
3/8-16 80.0 lbf-in 12.0 lbf-in
7/16-14 100.0 lbf-in 16.5 lbf-in
1/2-13 150.0 lbf-in 24.0 lbf-in
9/16-12 200.0 lbf-in 30.0 lbf-in
5/8-11 300.0 lbf-in 40.0 lbf-in
3/4-10 400.0 lbf-in 60.0 lbf-in
7/8-9 600.0 lbf-in 82.0 lbf-in
1-8 800.0 lbf-in 110.0 lbf-in
1-1/8-7 900.0 lbf-in 137.0 lbf-in
1-1/4-7 1000.0 lbf-in 165.0 lbf-in
1-3/8-6 1150.0 lbf-in 185.0 lbf-in
1-1/2-6 1350.0 lbf-in 210.0 lbf-in
Unified Fine
3-56 32.0 oz-in 7.0 oz-in
4-48 48.0 oz-in 10.0 oz-in
6-40 6.0 lbf-in 1.0 lbf-in
8-36 9.0 lbf-in 1.5 lbf-in
10-32 13.0 lbf-in 2.0 lbf-in
1/4-28 30.0 lbf-in 3.5 lbf-in
5/16-24 60.0 lbf-in 6.5 lbf-in
3/8-24 80.0 lbf-in 9.5 lbf-in
7/16-20 100.0 lbf-in 14.0 lbf-in
1/2-20 150.0 lbf-in 18.0 lbf-in
9/16-18 200.0 lbf-in 24.0 lbf-in
5/8-18 300.0 lbf-in 32.0 lbf-in
3/4-16 400.0 lbf-in 50.0 lbf-in
7/8-14 600.0 lbf-in 70.0 lbf-in
1-12 800.0 lbf-in 90.0 lbf-in
1-1/8-12 900.0 lbf-in 117.0 lbf-in
1-1/4-12 1000.0 lbf-in 143.0 lbf-in
1-3/8-12 1150.0 lbf-in 165.0 lbf-in
1-1/2-12 1350.0 lbf-in 190.0 lbf-in

Metric Thread Size

Thread
Size
Maximum Locking
Torque
Minimum Breakaway
Torque
Metric Coarse
M2X0.4 0.12 N.m 0.003 N.m
M2.2X0.45 0.14 N.m 0.02 N.m
M2.5X0.45 0.23 N.m 0.06 N.m
M3X0.5 0.45 N.m 0.10 N.m
M3.5X0.6 0.68 N.m 0.12 N.m
M4X0.7 0.90 N.m 0.16 N.m
M5X0.8 1.60 N.m 0.30 N.m
M6X1 3.00 N.m 0.40 N.m
M7X1 4.50 N.m 0.60 N.m
M8X1.25 6.00 N.m 0.80 N.m
M10X1.5 10.50 N.m 1.40 N.m
M12X1.75 15.50 N.m 2.20 N.m
M14X2 23.50 N.m 3.00 N.m
M16X2 31.50 N.m 4.20 N.m
M18X2.5 42.00 N.m 5.50 N.m
M20X2.5 54.00 N.m 7.00 N.m
M22X2.5 67.50 N.m 9.00 N.m
M24X3 80.00 N.m 11.00 N.m
M27X3 94.00 N.m 12.00 N.m
Metric Fine
M8X1 6.00 N.m 0.80 N.m
M10X1 10.50 N.m 1.40 N.m
M10X1.25* 10.50 N.m 1.40 N.m
M12X1.25* 15.50 N.m 2.20 N.m
M12X1.5* 15.50 N.m 2.20 N.m
M14X1.5* 23.50 N.m 3.00 N.m
M16X1.5* 31.50 N.m 4.20 N.m
M18X1.5* 42.00 N.m 5.50 N.m
M20X1.5* 54.00 N.m 7.00 N.m
M22X1.5* 67.50 N.m 9.00 N.m
M18X2 42.00 N.m 5.50 N.m
M20X2 54.00 N.m 7.00 N.m
M22X2 67.50 N.m 9.00 N.m
M24X2 80.00 N.m 11.00 N.m
M27X2 94.00 N.m 12.00 N.m
M30X2 108.00 N.m 14.00 N.m
M39X2 150.00 N.m 20.00 N.m
M36X3 136.00 N.m 18.00 N.m
M39X3 150.00 N.m 20.00 N.m

Notes:

  1. 12-24 is not specified in the NASM8846
  2. Unified Locking CoilThread inserts (Tangless and tanged) produce locking torques in accordance with NASM8846 when installed into 3B STI threads, and tested with heat treated cadmium-plated bolts.
  3. Metric Locking CoilThread inserts (Tangless and tanged) produce locking torques in accordance with MA1565 when installed into 4H STI threads, and tested with heat treated cadmium-plated bolts.
To Convert From To Multiply by
N.m ozf-in 141.6119
N.m lbf-in 8.850748
ozf-in N.m 0.0070615
lbf-in N.m 0.1129848