5 inputs determine the right push-to-connect fitting.

A distributor-facing pre-quote checklist. If the customer answers most of these at the first call, the second call is the quote.

1. 01
   What's the operating pressure and temperature at the connection point?

   Sets the body material tier on every fitting. Composite PTC caps at ~150 PSI — above that, the spec moves to brass (~230 PSI) or stainless (~290 PSI). Get the actual service condition, not the system plate.
2. 02
   What does the connection touch — food, drug product, instrumentation gas, normal plant air?

   Drives the regulatory branch. Food contact → NSF or stainless. Pharma / dairy → stainless. The wrong material in a regulated circuit is a failed audit, not a "premium upgrade."
3. 03
   What's the area classification at the install location?

   Class I Div 2, ATEX Zone, IECEx — any of these flip the entire fitting spec to certified construction. ATEX-certified technopolymer PTC is the answer for hazardous-classified pneumatic connections.
4. 04
   What's the tube material and OD, and is it metric or inch?

   Push-to-connect fittings are tube-OD-specific — 4 mm and 1/4" are not interchangeable. Stainless or hard tube generally needs a stainless or compression fitting, not a composite PTC. Get the OD measured with a caliper and the metric / inch call confirmed before pulling part numbers.
5. 05
   What's the thread type and size on the port end?

   NPT, BSPT (R), BSPP (G), Metric — composite PTC offers the broadest thread coverage; brass and stainless typically narrower. BSPP and BSPT look the same to the eye and don't seal together — confirm with a thread gauge or the OEM port spec, not by visual identification.