All EMCO Maier made milling tables for the Unimats are identical except for on dimension. They are cast iron. The edges are as cast with a slight belt sanding on the upper edges. The top and bottom are Blanchard ground so are pretty much parallel with a fairly smooth surface. I have seen a very few with the edges painted, most are not. Most I have seen have been black oxided. Some are in as cast and machined surfaces (gray and silver). The four edges may or may not be very square to each other.

The overall size of the one I measured is: 4 3/4" long x 3 1/8" wide at the top surface and a little more than 1/2" thick. The bottom surface is a little smaller as there is casting draft - the sides taper top to bottom. There is no reason why you could not make it 5" x 3 1/2" x 1/2". Remember that this thing is cantilevered off the cross slide so don't get carried away with the over size thing.

There are 3 T-slots in the top which are parallel in the long dimension. The outer slot centers are about 15mm from the edge. The center to center distance of the slots is about 25mm. The narrow part of the slots is 8mm wide. The bottom of the slots (the 'cross' of the T) is close to 18mm wide. The bottom of slot (the cross of the T) is: for DB/SL about 2.8mm and for U3 is about 3.8mm. The depth of the bottom of the slot (from the top surface) is: for DB/SL 7mm and for U3 8mm.

The mounting holes are on a square pattern 25mm center to center with two holes between each pair of slots. Two holes are 22mm from one end edge. The four holes are M6 clearance and are counter sunk (flat bottom) 8.2mm deep from the top surface. The mounting screws (2 M6 x 12.5mm). The counter sinks could be a little less deep if longer SHCSs are used. You do not want the screw to bottom in the slot before the screw is tight but on the other hand you want the maximum length of screw thread in the T-nut.

I agree that a good working milling table can be made on the Unimat without the T-slots. As has been recommended before by others, and I concur, a pattern of M6 (or 1/4-20) holes will work very nicely. If you go this rout please lightly chamfer the holes as burrs will be formed above the surface. An easy material to work is 6061T6 aluminum. Larger metal supply stores offer this in Blanchard ground fixture plate in 1/2" thick stock in may sizes. Using this material will give you good parallelism top to bottom and the edges are also ground. A very deluxe version could be made from precision ground flat stock in O2 steel plate, sold by Starrett and same but cheaper unbranded, in 1/2" thick x 18" long x 3" & 3 1/2" widths. The Starrett plate is toleranced. Thickness to + or - 0.001"; width to + 0.000/0.005"; Squareness + or - 0.001". Having the sides ground vertical and square to the top is a plus.

From post http://finance.groups.yahoo.com/group/UNIMAT/message/11300