Discovery mirror cell for a 17.5" mirror (18" may fit also). Made for a tube, but could possibly be modified for use in a truss scope. As I received it, the cell consists of a three-arm frame for attaching to the tube (1" steel (?) painted black) with threaded inserts in each end, and a thin-walled triangle (with a circle cut-out in the centre for addition of cooling fan) also painted black, which holds the mirror. At the flattened corners of the triangle are horizontal nylon set-screws for positioning the mirror laterally, and adjustable height mirror clips to ensure that your mirror doesn't flip out of the cell. The heavy-duty collimation bolts are spring-loaded and adjusted with wing-nuts. As currently configured, the mirror would rest on the three pan heads of the collimation bolts. I haven't used this cell, but would recommend adding some sort of a 9-point or 18-point triangle and bar floatation system. Should be a simple addition. The Discovery web-site lists this cell as a 9-point floatation cell, so either the cell has been changed since this one was made, or the previous owner (or one of them?) has removed the floatation system. Regardless, shouldn't be a big deal at all to add this. Cell looks brand new essentially. Sorry no pics, but happy to answer any questions! Cell sells for $179 + shipping from Discovery. Mine is $70 shipped or trade for ? Cheers!