Split nut unions are generally used to secure the hot tub heater housing to the spa plumbing. Screws are included. The actual diameter of the inside when closed (thread to thread) is approximately 2-5/16".
(Sold as a set of 2 complete Split Nuts.)
For example, if you type a 1 in the Quantity box, you will receive 2 complete split nuts - 4 halves and 4 screws.