PRP Pro Series CAS Bracket - Nissan RB20/RB25/RB26PRP Nissan RB Twin Cam Engine Double Pro CAS Bracket With Optional 20AN Head Drain Fitting. Our latest creation and evolution to our billet Cas bracket for the RB now includes a water fitting option to get water supply through the front of the cylinder heads largest welch plug hole. Ideal for dry block wet head setups running up to 20AN fittings, but also a viable option for engines in need of more cooling options through the front of the engine. The