Idle Jet O-Ring dimensions?

I recently posted inquiring about sources for these o-rings. Some nice peeps posted back up with
www.kz1300.com/forum/welcome-new-members...rubber-o-rings#23311

Looking at this link, it states the size as:
"Oring for Idle Air Needle 3.0mm X 1.5mm $0.75 each"

Other sources suggest 2.5mm x 1.5mm
Pic from Z1-Enterprises.com
 

I've bought kits from Keyster and Damien Ding  and have noticed that the O-Rings for at least the DD jets are loosey-goosey, to the point visible leakage is noticeable when back flushing using the Scotch Tool.

So now I'm wondering if the author from previous post  (use 3mm) had the same problem and went slightly oversize?
-or-
is 2.5mm really correct?

Thanks,

Don