Howdy,
1/2 pitch rims existed as 6 tooth, six spline and 7tooth, 7 spline (rare). The 6 tooth 6 spline was extensively used by Homelite. (All were made by Oregon). I was not aware an 8 tooth ever existed. It would have been huge! I doubt that the six spine clutchcup/adaptors for Homelite and McCulloch are available any longer.
There was a .404 8tooth, 6 spline for a while also. Most all of these 6 splines went out by the 1980's, The 1/2 pitch ones by the '70's.
Regards,
Walt Galer