Hardwood Floor Repair

[dark_arts]

I just put a new hardwood floor in my living room. It's a glue-down on top of luaun. My house is on pier and beam (it's old), and there are some small areas where the subfloor dips. I shimmed between the new floor planks and the luaun, but there are a few places where I didn't look to put in shims, and the planks sag slightly when I step on them. I know there's a kind of screw I can use to tighten the gap between the plank and the luaun that has a tip that expands when it's screwed in that should pull the luaun up toward the underside of the plank and push the plank down toward the luaun, but I don't remember what they're called. Does anyone know the name for them? Is it a roberts tip screw?