
Broken piece on bike-what is it and cheaply repairable?
I have a Giant Escape 3 and the circular piece I circled in red has come loose. It looks like it has four posts where it screws into the third gear but two of the posts broke yesterday.
I have no idea what to call this part. It looks like it's function is to catch the chain and slide it onto the final gear when shifting so the chain doesn't come off, but searching stuff like "chain guide" or "chain guard" yields different results.
It looks like I'd have to take the pedal off to swap if I can find a replacement, and I'm concerned this part only comes as part of a set with the gears and pedals in the first place. Are these things purchasable solo or am I better off just going to a bike shop?