2000 GTX/RFI Grease fitting size

[onesaintsfan]

Is the grease fitting on the flywheel of my 2000 GTX/RFI a standard size ( I.e. trailer bearing)? My grease gun fits fine on my trailer bearing buddy fittings, but I can’t get it to attach to the flywheel.
Looks the same but not sure. Tried and grease just comes out around it but won’t attach. If it is a standard size I assume then my fitting is clogged. How to clean or replace?
Thanks in advance

 

[tobytd]

5/16 hex…socket to remove
1/4 - 28 threads on zerk fitting
Don’t think it’s metric…COULD be wrong screw the replacement in slowly, carefully

 

[onesaintsfan]

Thanks . Ordered one of those grease buster tools and some extra fittings since I have a couple of other things need repair. But will certainly give that a go . Thx