Cassette mod required from a 10 speed to 7 speed

As i discovered, the cassette spline has different widths.
However, a thinner width cassette can still mount onto one that is designed for 10 speed if a lower speed cassette is used.

Here are the parts of a wheel

I got these used rims without the cassette.
These rims were used to mount on a Tern 10 speed.

I was looking for a 7 speed cassette to mount as my rear derailleur supported up to 7 speed.

Even though my shifter is now 6 speed, i have the option to upgrade the shifter to 7 speed.

Currently i have access from 11, 13, 15, 18, 21, 24 and reserve the 28T for next time.

The said cassette is a Shimano CS-HG41-7 (HG for Hyperglide)

As I discovered, the 10 speed cassette total width is thicker, so a spacer is needed to position the cassette properly.

I fabricated a spacer out of aluminum and filed tooth spaces to suit the splines.

Also because the cassette has 2 rivets, a recess is needed for the spacer to sit flushed.

As i discovered, my 2.5mm was still a little slack which allowed play on the cassette.
A 0.2mm shim ring is added on to close up this difference.

Now why didn't i go with 10 speed cassette?
To do that, i needed to upgrade the chain. But I don't want to do that now.

I hope this info benefits you the reader.

Thanks for reading.