The spool of a cartridge or cassette of web material is locked against rotation during shipping and handling by a "one-shot" locking member which has a fixed portion and a movable portion joined along a bendable connection. The movable portion is in engagement with the spool while the movable portion is mounted on the body of the cartridge. The locking member is released by bending the movable portion about the connection and stressing the material of the connection beyond its elastic limit. In one embodiment the locking member has a sector gear portion on its movable end normally engaged with a bull gear on the spool. In a second embodiment, the leaf-like locking member has a partially cut-out fixed portion intermediate its ends, joined to the member by a bendable hinge, and has ratchet teeth which engage ratchet teeth on the spool, permitting the spool to be rotated in only one direction while the locking member is engaged. A protuberance on the locking member extends into a pin access opening as a light seal and as a push surface for an operating pin. A frangible connection secures the movable portion in place and is broken during release and requires a higher intial force to disengage the locking member from its locking position than that required to bend the locking member about the hinge.