This Stainless Mesh Screen has a PTFE (Teflon) seal integrated around the outside of it.  The hard PTFE compount is highly chemical and heat resistant.  This can be used as a standard seal or alternatively it can be used as a filter screen preventing the flow of large prticulates going through your tri-clover fittings.

This fitting is often used for distillation to retain packing medial or used in pot distillation to retain botanicals in the vapour stream.