We generally recommend a fitting that can be re-swaged each time one of our columns is removed (both standard 4um and 2.o™ phases) to enable a clean connection when changing HPLC columns.
Permanently swaged fittings are not highly recommended, especially for columns with smaller IDs such as 2.1mm,  whereby any dead volume introduced can rapidly cause system performance concerns such as poor peak efficiency.

Any one or two piece, finger tight fittings will be best to use in a typical HPLC instrument if high pressure is not a strong consideration.

Never use PEEK fittings for UHPLC.

HPLC Fittings Ordering Information