Confirmat Screws in Dimensinal Lumber

[Terry Ezell]

I recently pickied up a bunk bed plan that calls for the use of Confirmat screws as part of the assembly hardware. Never having used these screws (except for when they came in a box of knock-down furniture) I hadn't given them any thought.

I have chosen pine dimensional lumber for my bed. The Confirmat screw threads are not much larger than the shank. I see how this might work well in materials that are compressed composites, but pine needs a little more thread bite in my opinion.

Is the 70mm Confirmat screw the best fastener to use, or should I go with something more traditional?

[Robert Reece]

I have used confirmats in plywood for shop things and they hold really, really tight. For fun I tried to strip the threads in the ply with my impact driver and was unable to do it, unlike a more traditional screw. I think the increased diameter gives you substantially more thread bite even though the threads aren't as deep.
I'd just do a little test in pine and see how you like it.

[Terry Ezell]

Thanks Robert. My plan calls for 70mm scrws, but I haven't really seen that size. HAve you used that size? Where do you get yours?

[Chris Friesen]

The Confirmat screw threads are not much larger than the shank. I see how this might work well in materials that are compressed composites, but pine needs a little more thread bite in my opinion.

Confirmat screws are designed to be used with a matching drill bit that has separate cutting diameters for the theaded area, the shank, and the head. Like this: http://www.cabinetmart.com/Confirmat-Drill-Bit.2455

[Robert Reece]

Terry-

I hadn't bothered to look up my screws until you asked. I bought them at McFeelys and they are 7x50mm. So 70mm is substantially longer than that! Those things are going to be beasts. Do they call for 7mm width?
And as Chris said, you do need a special drill bit that drills the required pilot hole and clearance hole in the mating piece.
I would not hesitate to use them as your plans call for. I'd still do a little test, but I would optimistically assume they are going to work fine.

[Ryan Baker]

Woodcraft carries both the 50mm and 70mm confirmat screws. I don't see any reason to use them in solid pine though.

[Chris Friesen]

Woodcraft carries both the 50mm and 70mm confirmat screws. I don't see any reason to use them in solid pine though.

They're sometimes used as quasi-knockdown fasteners for things that might get dismantled and reassembled a few times--like a bed frame. Lee Valley actually sells them as "knock-down screws" and specifically mentions using them in softwood--I expect because the physically larger size is less likely to strip out the weaker wood fibers.