If you your pump is NOT a Bosch MICO it is 18MM. If If has a MICO pump it is 14MM. I have run into a few that the bolts bottom out in the casting and thus won't seal. The easy check is to remove the line entitely. Then install the pump end fitting WITHOUT the seal washers and snug up the bolt. The line should be tight and not swing about easily. If it does you need to shorten the bolt.