That's an RB, (rotating back) series D Graflex. I had one, and they're a ball to use. The shutter curtain may be good, may not. It's about the only weak point. Better go to the Gaflex site for particulars, mine is long gone and I'll leave out some important step on setting the shutter speeds. Looks like the 3 1/4x4 1/4 version.