This is the Safariland ELS 34/35 kit that's popular with 3 gun competitors because of the modular capability it provides. When ELS 34 forks are installed on your rifle and pistol mag pouches and shotshell carriers, and ELS 35s on your belt, you can safely and easily configure your belt with only the equipment needed for each 3 gun stage. Why lug those big shotshell carriers around on a pistol/rifle stage?
These are compatible with Safariland ELS belts but I simply drill my CR Speed or Guga Ribas belt and mount the receiver plates directly to the belt.
Available individually for $8 or as a kit for $32.95 which includes 2 ELS 35 receiver plates, 2 ELS 34 forks and the necessary mounting hardware.