Here's the same banjo with another feature only found on inexpensive imported banjos:
It's a loop to hold a strap. Ordinarily, a strap mounting device is a good thing, but here, it's redundant because banjos have 24 hooks, any of which will hold a strap very nicely. Besides, these little loops rattle like crazy if you don't have a strap on them.
The strings are held in place by a tailpiece, which may be adjustable. This one is a "tension tailpiece" because it may be adjusted up and down to vary the downward pressure of the strings against the bridge:
Most resonator banjos and a few open backs have tension tailpieces. The more downward tension, the louder and sharper the tone, with a consequent loss of bass response.
Banjo bridges come in a wide variety of styles, some of which have even been patented, like this one:
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