When installing line cord cable in electrical box fittings, a slit, 1" length of fuel line tubing makes a fine strain-relief/clamp-pad, like so.
Pictured is 16/3 SJOOW[1] cable in a piece of 5/16" I.D. tubing. That combination fits nicely in an armored cable connector. The cable's jacket is firmly gripped, without being pinched, by the tubing.
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Note:
[1] 'SJOOW' is one of many designations of flexible line cord type.
SJOOW works out as follows:
S = Stranded (or Service) Cord.
J = Junior Service Cord. (Up to 300 Volts. Absence of a 'J' indicates Hard Service -- up to 600 Volts.)
OO = Both outer jacket and inside insulation are oil resistant.
W = CSA designation for a weather/water resistant cord.
