Atlantic's polypropylene bulkhead fittings install in flexible and rigid reservoir walls to create secure plumbing connections with standard Schedule 40 PVC fittings. Reverse threaded bulkhead fittings tighten as standard fittings are screwed into them. The 3" Bulkhead - FIPT has dimensions of 5.5"W × 2.5"H and has a required hole size of 4.5".