The monoball Fix Stop-Plate Kit for Pan System Rails from Arca-Swiss is for use with the 75, 150, 200 and 300 Cameraplates. The two flanges mount at any location on the rails by way of 1/4" screws. They provide a reliable stop for the accessories riding on the rail.
Use with Cameraplates 75, 100, 150, 200, 300