The William Optics "combo plate" — a saddle plate and dovetail plate sold as a pair — is one of the best value 3" width dovetail & clamp sets available in the UK. Other brands, such as Losmandy, are made in the USA and shipping charges and so on make them rather expensive here.
Unfortunately WO have chosen to make their dovetail a few millimetres wider than other 3" dovetails, and the clamp will not close up enough to grip a Celestron CGE dovetail or a Baader 3" dovetail. Furthermore, WO have changed the width of their dovetail. I have an earlier clamp that can grip the Baader dovetail, but is too narrow for the later WO dovetail.
WARNING: the following modifications will invalidate any warranty. You do them at your own risk. I will not accept any liability for any damage to your scope or other equipment. Use your common sense.
It is quite easy to increase the range of widths the WO clamp can accomodate, as long as you have access to a suitable workshop. The only part to be modified is the clamp block, shown in this picture.
All that is needed is to remove 1-2mm from the face that meets the clamp base, round off the corners, and increase the depth of the counterbore in the central hole. Take care not to damage the angled face that mates with the dovetail. The final picture shows the block ready to refit to the clamp base.
After this simple modification my EQ-6 mount can be used with both of my WO dovetail plates, the Baader 3" dovetail and the Celestron CGE dovetail. If anyone would like to give me a Losmandy rail to test I'd be happy to try it out.