1U high for two Boss Micro Studio series units side by side.
1U high. The UTR1 that Mercenary Audio sell does not look much like the photo or drawing on the Mid-Atlantic web site.
Don't own one so can't comment. 2-U version is Quiklok RS-674
Seems suitable for FMR audio's 1/3rd-width products (RNP, RNC, etc.).
Probably unsuitable for the Boss half-width units (Rxx-10).
Back in 2010-05, this rack cradle was not suitable for two Yamaha FX500 as it was too narrow and lacked the screw holes.
As of 2011-01, this SKU points to a different part. It has matte black paint instead of textured black paint and it bears a "Millenium" sticker. The holes are not quite the same. There is a cut-off in the front of the bottom (probably not deep enough for the Boss half-width units, though). There is a little more horizontal clearance and two FX500 now fit easily. The corresponding screw holes are slightly too close together but they can be enlarged with a needle file.
Holds two FX500. Yamaha product page says "discontinued".
Holds one FX500. Yamaha product page says "discontinued".
This is http://www.teaser.fr/~amajorel/cradle/, last modified 2011-01-08.