When installing our Spiderbeam Yagis or other directional antennas at the top of our aluminium push up masts, it makes a lot of sense to mount the rotator to the bottom of the mast, instead of at the top of the mast. Keeping the rotator and rotator cable down on the ground reduces the weight and stress on top of the mast, and of course makes it a lot easier to push it up. Keeping the rotator on the bottom also reduces the stress on the rotator itself.

There are a few different possibilities for mounting the rotator to the bottom of the mast (one example can be seen here http://docs.spiderbeam.com/rotator_mount.htm but is only possible with rotators where the clamps can be completely removed). 

Most rotators are only accepting mast diameters up to 63mm diameter, however our 14.5m HD / 18m aluminium push up masts have a bottom diameter of 80mm, which is the reason why we have designed this adaptor piece. All you have to do is drill a hole through the bottom of your mast, insert the 75mm part of the adapter into the mast, then put the bolt through the hole in the mast and the adapter and tighten the nut. 
Then you can insert the 60mm diameter tube into your rotator and start turning the mast.

tubes: aluminium.
Bolts & nuts: stainless steel
outer diameter of the top tube: 75mm
outer diameter of the main tube: 60mm
length: 250mm
weight: 0,6 kg