Radium 1/8" NPT Male to 3/16" Barb 90 Degree (4.8mm)

NPT (National Pipe Thread) fittings seal by the intentional interference created by the tapered threads meshing together.

Always use a small amount of PTFE paste or tape on NPT threads and tighten to finger tight, then add another 1.5 to 3 turns until tight.