1/4-28 grease zerk tap?

[MyLilMule]

Of course, you have always have drilled a hole in some scrap, tapped with a 1/4-28 standard tap, and test fit the xerk. Just sayin.

 

[Batmanacw]

The 1/4-28 tap worked perfectly.

I had to countersink the hole just a bit to allow the major diameter to fit into the hole since the threads weren't cut tight to the nut.