[Healeys] Oil pressure line fitting

[rjhco]

Mike Salter is correct.  The thread is 3/8" x 28 tpi. In the engine block.

3/8' x 24 is BSF (British) and UNF (US) fine thread for a machine
screw/bolt;
3/8" x 24 is also used in brake line fittings for the tube nut which
requires a 7/16" line wrench.
3/8" x 27 tpi is 1/8" NPT (US) - National Pipe Thread and is tapered
3/8" x 28 tpi is 1/8" BSP (British) - British Straight (or standard) Pipe
and is not tapered.  You should use a copper washer with the fitting.

Many owners force in the wrong NPT nipple into the block, which results in
oil weeping from the fitting.

Best regards,
Jim Hockert