Six Caps?

I suppose I'll feel dumb when I get the answer, but what kind of "caps" should a model kit have six of? (From the current Scale Auto "Tips" section.)

Caps

Tip: I’ve seen some model kits that only have five caps instead of six. An easy way to fix that is with Evergreen Styene Rod #211 (.040" diameter). Cut off the existing caps, drill new holes with a 3/64" bit, and insert short lengths of styrene rods for the new caps. Just add glue and you’re done. – Model Mikey via E-mail

Source: http://cs.scaleautomag.com/SCACS/forums/thread/977095.aspx

Ronnie Bucknum Ivor Bueb Sebastien Buemi Luiz Bueno Ian Burgess