Polyester multi-filamentary yarn, useful as tire reinforcement, is produced by melting polyester resin at 290 C. The cup has a first outside diameter, and the plate has a second outside diameter greater than the first outside diameter. This spring finger deflects out of the way permitting the window’s insertion, snapping back to engage a vertically extending flange on the window to retain it in the opening. Accordingly, unnecessary retrial processes of a drive system are reduced such that the performance of the drive system is improved and error correction capability is enhanced.