Ok. The seal I used came from a napa 3358 fuel filter. The oring is suppossed to go on the threaded post that the filter screws into.. The seal is 9/16 inside dia. 7/8 outside dia. and 0.015 thick and is square cut. I basically split the pump, cleaned the remains of the old seal and put the new one in the seal holder and it is still leak free after 2 years. The shaft dia. on my pump is 5/8. Hope this helps. I have a few extra seals if you want me to send ya one. Good luck!! Beats buying a new pump!