This is a stereo microphone bar designed to take clip-on lavalier micrphones and position them either in the ORTF configuration or in X-Y.
It was specifically designed to take cardioid Clippy microphones from FEL Communications using Primo EM-184 capsules, but other cardioid clip-on lavalier microphones should work as well.
If you are using Clippy microphones the ORTF spacing and angles will be correct, but the X-Y position doesn't result in a completely coincident pair. The capsules will be separated by about 30mm. Other microphones will have slightly different geometries that will change the positioning of the diaphragms.
Please be aware this will only create an accurate stereo image if the microphones being used have a cardioid pickup pattern. Omni microphones will result in a slightly spaced image when used in ORTF, but it won't be ideal. Omni microphones really need a wider spacing or a baffle to create a strong stereo image.
Supplies for building a pair of cardioid EM-184 Clippy microphones can be had from FEL Communications (Micbooster.com):
The three holes in the bar are sized for 1/4"-20 screws. The two outer holes are through-holes for mounting other gear on the bar. The center hole is threaded to mount onto a standard photographic tripod or light stand. If you want to use this on a microphone stand you will need an adapter (or just modify the thread to suit).