These receivers are required to allow the attachment Priefert's Wishbone Carriage (CA04-2 or CA04-2WT) to your Model S01, S0191, or S04 Priefert Squeeze Chute (carriage and chutes sold separately). Priefert's innovative wishbone carriage system is simply the easiest one-man chute loading system on the market and makes moving your squeeze chute a snap. The Model S04 Chute uses CRS04-2 receiver.