I find this Common Errors in English page very, very useful. It cleared up both the jerry-built/jury-rigged confusion and the whole tenterhooks question.

I direct my little brothers^* to alot and it’s/its; they are both afflicted with blind spots regarding these two.

^* For the record, I have three brothers, Mike, Johnny and Steve. Johnny and Steve are “my little brothers” as a collective noun because they are twins, and six years younger than me. Mike is simply “my brother” because he’s not a twin, and we’re very close in age. “My brothers” is a reference to all three of my brothers. And Johnny and Steve are “my brother Steve” and “my brother Johnny” individually. Complex, no? I have no idea how my brothers refer to me.