I found an old box camera in my grandfather's barn. It says its an R.B. Graflex and the last patent date etched in the bottom plate is May 3-13. I have only the courage to open the lens which shows it as a 4x5 bausch and lomb, zeiss tessar series 1c, patent 2-24-03, serial 2185900. The leather (?) handle on top is gone due to age. I only dusted it as I dare not try to use a cleaner on it. I am trying to determine its precise model and year of manufacture. Any help would be appreciated.

Look the body for brass plate. On it will say "curtain aperture" Somewhere, usually above curtain aperture, will be the model name.

sometimes the plate is on the viewing hood or chimney. There should be a clip or latch at the top front. (to state the obvious, the place where the handle was is the top.) The top hinges on the back of the camera. Open the top up and the chimney (or what's left of it, barns are usually kind to leather and wood) will open. It may even say on the front of the chimney.

Lenses on RB cameras are usually one format longer than normal. If the lens says 4x5, then I'm guessing your camera is a 3 1/4 x 4 1/4. But Graflex made at least half a dozen different camera models in that size

Another option is to search ebay for "Graflex" and see what shows up.