INTRODUCTION
SAE Markings for
Hex Nuts
Grade A-B-C
Locknuts
A (No Notches)
B (Three Marks)
C (Six Marks)
METRIC HARDWARE IDENTIFICATION CHART
Class
5.8
8.8
10.9
Hex Cap Screw and
Carriage Bolts
Located on the face or flat,
on the cap of the bolt
Located on the face or flat,
on the cap of the bolt
Located on the face or flat,
on the cap of the bolt
Hex Nuts and
Locknuts
Located on the face or flat
of the nut
Located on the face or flat
of the nut
Located on the face or flat
of the nut
Metric cap screws and nuts are identified by the grade number stamped on the head of the
cap screw or on the surface of the nuts. U.S. customary cap screws are identified by radial
lines stamped on the head of the cap screw.
DEFINITIONS:
1. Break-Away Torque - Torque measured in the direction of tightening, the moment before the bolt/nut starts to turn.
2. Clamping Force - Force equal to the tension in the fastener that clamps the parts together.
3. Stabilized Torque - Torque measured on a joint that has had a settling time after fastener installation, and the torque
is measured in the direction of tightening, the moment after the bolt/nut begins to turn.
4. Proof Load - Safe test load for fasteners, approximately 10% below the yield load.
5. Torque - Force on the wrench handle times the handle length.
6. Torque and Turn - Bolting method utilizing a torque sufficient to close the joint, followed by rotation of a specific
angle to obtain the desired bolt stretch.
7. Torque to Yield - Bolting method that tightens the joint until 0.2% yield is detected. Generally requires a computer
monitored tightening tool.
8. Target Torque - Torque specified by engineering, generally nominal torque.
9. Ultimate Load - Load when bolt failure occurs.
10. Yield Load - Load when 0.2% deformation occurs.
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