A lot, unfortunately...
Like 30 or 40. Well, I'm not sure offhand. It's to replace the screws on my square reactor (same as Jonathan's). I forget how many it uses, but it is something silly like that. When we built these units we kind of went overkill with the drilling. I'll say this: the reactor doesn't leak from the gasket that's for darn sure. But it's a painfully slow process using a screwdriver to undo them all and redo them all when it comes time to replace the media. So I thought I'd take the opportunity (since I have to put new media in anyhow) to put in some thumbscrews instead.
Anyone know of a place one could MO them if there isn't a local store that sells them? I only see the traditional slot-head type screws over at Rona and Home Depot.