View Full Version : Help.. Need some fastener ideas

04-13-2009, 09:10 PM
I need to mount some plates with posts to a floor that I have no access to the underside of. The flooring is roughly 5/8 flooring board topped with 1/4" tile subsurface board and 1/4" tile ( roughly 1.125 - 1.25" thick)

No, I can't get into a stud.

I have these types of anchors, but I want something stronger and easier to use. Any ideas and sources for something stronger?

It'd be nice to have a hex head instead of screwdriver slots, and a hex to hold onto on the topside as the underside of the fastener cinches up.





04-13-2009, 09:45 PM
Would it be worth your while to create access to the underside by cutting a hole in the floor that could later be patched?

04-13-2009, 10:42 PM
The only other option I know of is a blind nut but they wouldn't hold well in wood. I suggest you make a mounting plate. Fasten the plate to the floor with wood screws then fasten your post plate to it. Or mount your post plate directly to the floor with lag screws (bolts).

04-13-2009, 11:08 PM
How about some wood/metal dowels? 5/16 dia and 2 1/2
inches long,or 1/4 x2 1/2 .. 1" lg woodthread on one end
and machine thread onthe other.. drill pilot hole and set
with two hex nuts,remove lock nuts ,drop on washer add hex nut and ratchet down

04-13-2009, 11:24 PM
Like these:


I don't know how they will hold in wood but they have the other two requirements; hex head and flats to hold the "expander".


04-13-2009, 11:44 PM
What Herb described might work the best. They are called 'hanger bolts' and are available from any good fastener store and are available in just about any size and reasonable length.


04-14-2009, 12:15 AM

Haven't tried these, but they look promising...

- Bart

bob ward
04-14-2009, 02:34 AM
What forces do the fixings need to withstand? Are they purely locational, ie to stop the bottom of the post from moving around, or is there an uplift component to consider?

Paul Alciatore
04-14-2009, 03:23 AM
As Bob said, it would be really good to know what you are mounting. What kind of forces will they see; tension, shear, or what? And are you limited in the number and size of the screws or can you add additional ones to help take the load? Other choices would include plain wood screws, toggle bolts, threaded inserts, etc. Many possibilities.

04-14-2009, 07:14 AM
For the largest spread on the underside you could look at toggle bolts - might have to check if strong enough though...

04-14-2009, 09:00 AM
If it is a handrail post (which it probably is or you wouldn't be asking) whatever you use will look like a 3' crowbar trying to pull the anchors out because that's what it is. I won't even use wood blocking between two joists any more, I fab a steel bracket that bolts to two joists.

04-14-2009, 09:15 AM
Barrington's suggestion of toggle bolts is probably the simplest and strongest. I have some that are 3/8"-16. They require a 1" hole to pass through, and the nut portion is kinda stingy. However, if you ran a bolt UP through the toggle, threaded a fender washer over it after insertion, and a hex nut to clamp, it would hold well. Question: what is wrong with the Screw Mollys? They are available, (I think,) in 1/4"-20, and four of them on a plate would be FAR stronger than the plywood floor that they are fastened to. A bit of a pain to install, but life is never easy or we would have nothing to talk about!