You are correct about the seals/shields. MRC elects to use Z to designate seals whereas most mfgs. use it to designate shields. C2 internal clearance is actually tighter than normal. Most mfgs. use no designation or C0 to designate normal with C3 being looser and C2 being tighter. Some mfgs. use EM to designate electric motor quality which will include C3 internal clearance or will designate it as C3. If it doesn't have one or the other or some other designation (C4 for example) you most likely have a normal clearance.