Insert

[1] When referring to bearings it indicates a replaceable shell-type bearing made to extremely close tolerances and generally used for main bearings and connecting rod bearings.
[2] When referring to valves it indicates replaceable valve seats made of hard, heat-resisting metal that are screwed or shrunk into the cylinder head.
[3] When referring to spark plugs it indicates replaceable threads which are installed into damaged spark plug holes so that spark plugs can be installed. Sometimes known by the trade name "Heli-coil".
[4] Piston liners or cylinder sleeves.
[5] As a verb, it is the technique of permanently joining plastics and other materials, e.g., embedding steel clips in a molded plastic cover. Molded-in inserts are placed into the injection mold cavity so that the melt flows around them during injection; post-molding inserts may be installed by press-fit or ultrasonic methods.
See also bumper insert, groove insert, precision insert bearing, thread insert, top ring groove insert, valve seat insert