These are hand laid-up couplings either female by female threads, or half couplings made with Hetron 922 resin with an MEKP cure. They contain no fillers or pigments, and are machined to a uniform outside diameter.
These couplings are similar to the standard couplings, but are made with an isophthalic polyester resin. This resin is for areas requiring lower levels of corrosion resistance such as water or brine service. This is a less expensive resin.
This is different cure process for special applications, such as sodium hypochlorite. The resin is Hetron 922, but the curing agent is BPO-DMA. This produces a more corrosion resistant part, for these applications. The liner is a double nexus and double c-veil liner.
The stepped coupling is specifically designed for the tank fabricator that wants a half coupling with female threads on one end, for glassing into the side wall of a fiberglass tank. This coupling, in conjunction with a properly sized hole, will stop with half of the coupling projecting from the sidewall due to the step in the coupling.
The CT, cone tapered, coupling is similar to the stepped coupling just above, and is designed for mounting to the sidewall of a fiberglass tank. In this case the coupling is designed to minimize the lay-up required to tapper from the coupling to the sidewall of the tank.