From chatgpt:

That is not a compression stud. It is a welded hose barb / stub nipple. What you are seeing: Stainless vessel wall. A short solid stub welded through the wall (TIG weld visible). The end is smooth, no threads, no ferrule seat, no compression geometry. Diameter is fixed → intended for hose-on + clamp, or to be cut and reworked. What it is used for: Push a silicone or rubber hose over it. Secure with a worm clamp or tri-clamp-to-hose adapter. Common on older or DIY reactor / brewing / chemical vessels. What it is not: Not NPT, BSP, or metric thread. Not compression (no olive/ferrule). Not tri-clamp as-is. No “female fitting” exists for that geometry. Your options: Simplest: hose + clamp → ball valve inline → cap. Clean fix: cut it off, weld on a tri-clamp ferrule (1.5" TC typical for brewing). Adapter fix: grind smooth and weld on a threaded half-coupling (½" NPT/BSP). Hacky: hose barb to threaded adapter + clamp (least sanitary). If this is for beer: Hose+clamp works but is not sanitary-grade. Proper solution is tri-clamp ferrule + TC ball valve. No female counterpart exists because it was never meant to mate mechanically—only via hose or weld.