This fitting is 1/8 NPT to 1/4 inch OD tubing compression. 

Manufactures recommendation for tightening the compression fitting on to the nylon line is hand tight plus one turn. Tubing must be cut square (maximum 15 deg) for effective sealing.

NB: A thread sealant is required on all NPT threads.  Matco recommend Loctite 567
(we have had great success with 'Fuel lube')