shear strength of “square drive screws”
jwcamelshump
| Posted in Construction Techniques on
I’d like some help trying to settle a debate between one of my partners and myself. We sometimes use primeguard square drive screws in our framing for very small jobs or when it is difficult to get a framing gun or hammer into a tight spot. He claims the brittleness of the coated primeguards (they snap pretty easy when you hit them with a hammer, but are very hard to cut) gives them very little shear stegnth. I think the threads and diameter of the screw are more than adequate. Does anyone out there have information or can you tell me where to find out about the shear strength of these types of fasteners. Thanks
Replies
Was that a Can-O-Worms opening?
If you do a search on Screws Vs. Nails here and my username, you will find a thread I started on the topic awhile back.
I am a BIG proponent of using screws, but with care as not every screw is worth a darn. Screws made by Grip-Rite, from what I've seen, are not worth a darn. Instead of those, look at the Deck Mate Square Driv screws, made by Phillips and available at both Lowes and HD. From what I've seen, they just use a better quality of steel in their screws. They are strong without being brittle. You can whack them with a hammer and they just bend over. I've witnessed their #9 screw have the shear strength to tear 16ga. steel Simpson strap in a pull apart shear test.
If you are using connector hardware, Simpson just came out with their SD9 and SD10 screws (no, they are not the 1/4" lags or #8 wafer head screws that they've had for awhile!). They have a 1/4" hex head, and drive like a dream.
I like to make sure the screws I use are diamerter similar to the equivalent nail size... that means no #8 screws for framing lumber! They just don't have enough cross section. Insead, look at #9 and #10 from GRK, McFeeley's, and Screw Products... all three are great companies.
For your buddy who thinks whacking screws is a valid test, try this: Take a couple short chunk of 2x and screw it into a stud with a single #9 Deck Mate. Do the same with a 16d nail, glue coated, ring shank, spiral, whatever you think is the best. Now try and whack the board off the stud with a hammer... I bet I know which one comes out first!
Instead of paul's non astm standard testing.
contact gripright and ask for a printout on shear strength etc. If they submitted their screws for testing, they should be able to back it up.
If they didn't submit-then it's safe to assume they don't recommend their product for framing where shear strength might come into play.
This is not to say that they wouldn't hold up, just there's no building inspector backup if that should become necessary.
How are your fasteners being used? Length makes a big difference in plate fastening, but thickness and the strength of the metal/ga. are what is of concern in ledgers and beams.
Yep, some "deck" screws are
Yep, some "deck" screws are quite strong, others incredibly brittle. For stuff that needs to be reliably strong (which is not true of most framing), I use GRKs.
If you look at most framing gravity does 95% of the work and the fasteners are there primarily to keep the parts from slipping apart. Aside from possible seismic/windstorm issues, no significant strength is required.
The manufacturer lists them for all exterior applications
this include deck structures and playsets. Both of which have moderate loads. Playsets actually have pretty high cyclic loadings from swings.
I've been using kreg's pocket hole screws for few years now. I'm sure they are as stout as a toenailed nail.
For a "toenail" connection,
For a "toenail" connection, I'll take a 1/2" spade drill bit and set the point at about 1" above the board end. Then instead of drilling straight in, I'll push the point in just enough for it to catch - then I pivot the drill and lay the bit side into the wood creating a "pocket" for the head of a pan or washer head screw. The pocket has a flat seat for the screw head too, and doesn't split the end grain.
You need to use round washer head or pan head screws though, flat head screws will blow out the end grain.