The squeeze between the clamped parts that results from bolt preload. With no external load the two are equal and opposite; when the joint is pulled apart, clamp load drops while bolt tension rises only slightly, because the stiffer joint takes most of the change. Friction from clamp load resists shear slip in slip-critical connections and keeps gaskets sealed.
Gasket wants twelve thousand pounds of clamp load per bolt, and at forty foot-pounds dry we're nowhere near it.
Also heard as
- clamping force
- clamp force
Do not mix it up with
- Preload: Preload is the tension in the bolt itself; clamp load is the compression it puts on the parts.
Related terms
Preload
The tension created in a bolt by tightening it, which clamps the joint and keeps it from slipping or opening.
Embedment
Preload lost soon after tightening as surface roughness under the head, nut and threads flattens out.
Belleville washer
A dished, conical spring washer that flattens under load and keeps clamp force on a joint as it settles or expands.
Torque-tension
The relationship between the torque applied to a fastener and the preload it produces, dominated by friction.