These adaptors are for the S-33 Gearcase Filler. All adaptors have a standard 3/8-16 female thread.
Don't forget that some Mercs & Evinrudes have Yamaha or Suzuki fittings!
Gearcase Filler Adaptors
Part No. Description 334Y 8mm for the metrics (Honda, Yamaha) 334Z 10mm for Suzuki 33DP OMC/Volvo duoprop 33X Extension, standard 3/8-16 for Merc Bravo