Optical parts
The only optical parts to be used are a laser (I have a red one), a small 50/50 beam splitter, a small biconvex lens and a small flat mirror, which I all purchased from Surplus Shed. There's no need to use high quality, expensive optical parts because of the 'common path' design (see literature). Dimensions of the parts I used: beam splitter 15x15x15 mm, BCX lens 6 mm diameter f/0.67, flat mirror 12.4 mm diameter and 6.2 mm thickness (my 20 inch mirror would be 10 inch thick if it had the same diameter/thickness ratio). The distance between the two beams - should best be kept within 8 millimeters - is 6.25 millimeters. After I made the first two pictures I added a 1000 ohm potmeter to the setup, to be able to dim the laser (can be seen on last photograph). Now I can look at the fringes naked eye. For the layout drawing of my interferometer click here

mountings
I made the mountings from square 15x15 mm aluminium tubing, to which I glued an M8 bolt to mount the parts on the 103x78 millimeters (hard) wooden base plate. The mirror, lens and beam splitter are glued to their aluminium mounts with 1 mm thicksilicone adhesive. To be able to move the lens in X and Y directions I used delrin, sliding smoothly -without having room to make unwanted movements - in and out the aluminium tubing. Aluminium parts were glued together and to the wood with a two component metal epoxy. The blue knobs are in the pictures are fastening knobs, except for the one just below the lens, which is meant to rotate the lens a little around the X-axis.

XYZ-stage
On the picture below, the Bath interferometer is mounted on the XYZ stage. For the Y-movement I use an old focuser. The XYZ-table is relatively heavy, but this has the advantage of being very stable and not having to be very cautious when switching the interferometer on/off or manipulating the direction controls.