Our Telescope Clamps requure an accurate measurement of the diameter. A mm or so incorrect measurement way mean the clamp is too big or too small.

The best way to measure your optical tube is to use a pair of digital calipers.

The worst way is to use cloth measure tape, measure the circumference and divide by 3.14 (pi). We tried this ourselves and we couldn't get it accurate to a few mm, so we do not recommend this method at all.

Tripods are easier to measure, most EQ6 tripods are 2", most EQ5 tripods are 1.75". We have no issues going down to 1.25" or up to 2.5". We do not use felt in our tripod clamps as we don't feel it's needed.