Clamp Needed for Carriage on Profile Rail

[diamondcat]

I am using Thomson Carriages which are rolling on profile rails. There is another company that sells manual clamp units that bolt to the back of these type of carriages. This allows the operator to stop and lock the carriage at any point on the rail. I do not remember who sells this item and I can't seem to find it when searching on the web.
I was wondering if anyone has seen this item and could direct me to the company that sells it.

Thanks,
Lori