Rick: That would be a tough one to find. But, after seeing some of the mistakes at our oil/fuel filter plant, I can see how it would happen.
We have one filter that has a solid plastic bottom cap, the paper filter element, and a plastic top cap with a raised nipple. It's a diesel fuel filter, and goes into a welded plastic housing. The fuel enters around the outside, goes through the paper, and exits through a hole in the nipple. Very simple. The assembly people have to manually insert the end caps, and the have two boxes, one on each side of the operator, feeding two conveyors, one on each side. Top caps on one side, bottom on the other, very simple. All filters are manually inspected at the end of the oven, where the glue is baked to set it. Then they're sent into the "clean room", where I put the housings together.
The nipple snaps into the top of the housing, with two hose ports, and a bowl covers the bottom. I grabbed a filter a few months ago, and it wouldn't go into the top. They're supposed to be put in the box top up, but every now and then one is upside down. So I flipped it over (without looking at it) and tried again. No luck. Looking at it I saw that it had two bottom caps... Obviously not only the operator but the inspector weren't paying attention that day...
Missing an uninsulated wheel would be a LOT easier, and if they feed automatically, nobody would ever see it.
Whatever the advantages of metal wheels, that's one problem that won't happen with plastic!
