The Century JJ is the only Century projector that can project both 35 and 70mm.
Potential Damage: The Century JJ can run a print several hundred times without any damage, but special care much be taken to by the projectionist and technicians. The most common form of damage caused by JJs are slap scratches, which appear as small tic marks on screen, usually in clusters if a print has been run several times on the same projector using the same threading pattern.
Slap scratches occur in two areas: the upper and lower loop. In the upper loop, 70mm prints can get slap scratches by hitting the upper 35mm roller, especially if the loop is too small. To avoid this, remove the 35mm roller and replace with a second 70mm roller. The lower loop is more complicated. Most Century JJs have a roller underneath the intermittent that acts as a stabilizer and prevents the film from hitting the top of the intermittent casing. Some projectors have additional rails that work to stabilize the lower loop, and consequently make it run quieter.