An I-beam clamp, used for engaging the bottom flange of an I-beam or bar joist, includes a pair of threaded rods and a pair of brackets that can be moved relative to each other along the threaded rods. Each of the rail members has a multiple piece construction including first and second interlocking synthetic rail pieces and a metallic reinforcing insert. A portion of the MEMS device includes an acoustic area, an acoustic seal area that surrounds the acoustic area and includes the acoustic seal, and electrical interconnect area that are located outside of the acoustic seal area and include the bond pad. At least one of reflecting surfaces and an exit surface of the prism 4 is shaped as a rotationally asymmetric surface which exerts a power on bundles of rays, to compensate aberrations generated by decentering. , that may be of interest to the viewer.