Pressed frit filters contain a permanently installed stainless steel 2µ frit, and are recommended for applications where contaminants are the exception and not the rule - that is, when the sample is generally clean but you wish to guard against the stray burr from a carelessly prepared tube end that might find its way into the flowpath.
Bulkhead versions are designed to be mounted through an instrument panel or on a bracket. The filter body is undercut so that it bites into the panel when the mounting nut is tightened, eliminating the need for a lock washer.
Standard material is Type 316 stainless.