zerk (grease fitting, or nipple) size identification

[Kayaker37]

this is on a B2660 snowblower, missing a zerk fitting on the mid driveshaft in the universal joint. the fitting is shown as part of a 70050-93250 repair kit which is the whole assy, just need the fitting. Napa took calipers to the fitting I handed them from the other end and a thread checker, but when I got home it won't fit. my eyes aren't good enough to see the threads, but they measured it at 1/4 28, but in comparing (after taking a picture and enlarging) I have about 3.5 threads to 3 of that, and slightly smaller. anyone know what the correct size would be?
in the picture the correct fitting is at the bottom, 1/4 28 at top which is too big (although that size is used on the auger, so would they mix metric and imperial sizes?)

thanks to everyone for all the help,
Paul

 

[G.rid]

I don't know about your blower, but the next semi-common size would be M6 x 1mm. That would be slightly smaller in diameter (.0138") and slightly finer pitch (.0037"). I have come across a zerk from a off shore Massey that was M6 x .8mm. Same diameter difference but the pitch would be even finer still (0.0042"). It doesn't sound like much but it won't go easily.
You always have the option to retap the hole out to 1/4-28 and make them all standard. Just be sure to get all the chips out.

 

[Kayaker37]

I realized after some googling last night it is part of another piece that makes up a 45 degree angle, so looks like I may have to unscrew a remaining ball piece, and replace both at the same time.