Fine thread screws for hardwood?

[Chris_B]

This may be a dumb one, but...

I have never understood why it is important to use fine thread screws in hardwood. I have stripped fine screws in softwood, but have never experienced strength issues using coarse screws in hardwood. I am sure they are somewhat stronger, but overall the coarse screws seem to hold just fine when I have needed to use them.

I *especially* do not understand this with pocket screws, since they are essentially local clamps, and the glue provides tremendous strength.

This question surfaced when I needed to order more screws today. Doubling my P/N's significantly increases the odds that I will run out of inventory at inopportune times...

Thanks,

Chris

[WayneJ]

I've used coarse thread in all my projects,mostly oak and never had any problems. As long as you use pilot holes you should be fine. Come to think about it, I don't have any fine thread screws in my supplies. I have used them to go into steel 2x4s on a wall.
Wayne

[Wood_workur]

beacuse the fine threads have more holding strenght, but in coarse threads, the space between the threads is bigger, allowing the wood there to have more strength.

[Tom Miller]

I thought it was because the coarse threads were more likely to split the wood, since coarse threads usually make up more of the diameter of the screw.

Regards,
Tom

[vaking]

I was not even aware of a rule for fine thread in hardwood but if it is a valid rule - Tom's explanation seems the most plausible. The former mechanical engineer in me says that (at least in metals) no matter what type of thread you use only the first few threads accept the real load. The engineers textbooks say that the first thread typically carries 60 - 70% percent of the total load on the screw. If you put to much load - the first thread will strip and will transfer the task to the next. Because of this coarse threads are actually stronger that fine threads. Fine threads provide more precision and some other benefits though.