[Fot] 26 spline diameters?

[MadMarx]

Hi Guys,

I want to equip my TR8 with new clutch discs.
The car has a triple clutch.
Now it is getting funny.
I measured the splines and found 1-1/8" 26 spline version.
It seems now that this type is named 1-5/32" 26 spline.
And unfortunately there are real 1-5/32 ones available and some which are
1-1/8".

How can this be that two diameters are sold under one size?

BTW....PTT clutch is installed.

Cheers
Chris