What brick is this? 1x2 with holes in the short sides
This is part 3317.



It's primarily used to hold the bucket on front end loaders. It hasn't been used in a set since the late 90's. Part 3314 is about the only other part that is designed to connect to it that I'm aware of:



Here's an example of this part in use from set 6504:



While I believe that this was the only way to connect to this part used in official sets, I'm sure it may have other uses. It was used to build gas pumps in one set: