Quoted from MarkG:
Shorter #55 bulbs were sometimes used in pop bumpers to move the filament away from the bumper cap. It helped keep the cap a bit cooler and may have avoided the common burn spot on the underside of the cap. Cooler #47 bulbs are another option.
Agree with using the 47s and that's what I put in this machine. finding 2 - 455s threw me off. Thanks for the post!
Now anyone with 4 of the pf screws or know where you can purchase them? Would prefer the original to the newer Phillips ones.