can anyone tell me what size the primary gear nut is on my 76 DT400?  My 27mm is just a bit to big and it's the smallest big socket I have, if that makes sense, so it looks like there's a new socket in my very near future.  Thanks, Tony

I don't know the exact answer offhand... I have a socket that fits but don't remember the size.

Just wanted to mention if nobody answers you can determine the socket size on metric and standard nuts by measuring the nut across the flats. 

(Unless it was an old British bike...  they used "Whitworth" tools where the diameter of the bolt threads was used for the wrench size)

Thanks Mark, I'm thinking it has to be a 26mm but want to be sure before I go out and spend money. I did try a standard socket on it, a 1 1/16 that was about the same fitment as the 27mm. If all else fails I'll try your suggestion.

A 1" socket would be 25.4mm

1 1/16" would be 26.99mm

So if 1" is too small, and 27mm (or 1 1/16") is too big, has to be a 26mm.

 

Thanks again Mark! My smallest big standard socket is the 1 1/16, I looked to see if I had a 1" but that was a no go. I may go and see a mechanic friend to see if he has a 26mm he can loan me so I'm not just spending money and it not work. Having said that I just don't see it being a 25mm but I've been wrong before...

if it is like my DT360 then the primary was 26mm and the clutch 29mm
and i thought i had all the sizes!

Thank you Msavitt, I'm sure they are the same and mine is a 26mm too.