Not sure of the thread depth without getting into a lot of technical lookup, but 3/8-20 is not a standard thread that i've found.  3/8-16 NC or 3/8-24 NF maybe, but unless you are specifically ordering a 3/8-20 (which you can), i would stick with one of the standard SAE sizes found in most stores and tap/die sets.

 

Borrowed the following from Victornet...  these assume about a 75% thread and that you have a rather complete set of bits to drill  with.

Coarse

1/4-20     #7

5/16-18    F

3/8-16      5/16

7/16-14    U

1/2-13      27/64

9/16-12    31/64

5/8-11      17/32

Fine

1/4-28     #3

5/16-24    I

3/8-24      Q

7/16-20    W

1/2-20      29/64

9/16-18    33/64

5/8-18       37/64

Good idea Dan.

3/8x16 is course thread and 3/8x 24 is fine

Dan is showing what you need either in 5/16 or 3/8 bolt size either one would be strong enough.

Many years ago my wife wanted a small quilt rack. I looked at some and created my own. I threaded the Oak at every connection and put big spinner type handles for easy tightening. It worked really well. I put spreaders on each side of the quilt and made a tools holder too.

 Threading wasn't too difficult, do it carefully and slowly

Years ago the owner of Lee Valley started a magazine called Wood Cuts. In it the had an article about using machine screws in woo and found that with a properly sized hole the machine screw held better than a wood screw.. Now as to tapping I have only tried effectively to tap either 1 inch or 1 1/4. The 1 1/4 I have a beall tap for the lathe and it works great. As to strengthening the threads with CA yes that does wonders and then run the tap thru again. I think that with end grain the threads will break out easily.

experiment w/ the hole size and use a type ""F"" tipped screw...

lots and lots of head styles...

 

Edited March 2, 20188 yr by Stick486

You can always use a 3/8" dia. lag bolt. I have used them many times on large wooden tables and they hold great.

Herb

12 hours ago, Ron Dudelston said:

Here's my question, Gene.  Is there a reason you are using a fine threaded bolt.  A standard bolt is 3/8-16

No reason other than ignorance. Since my first post though, I found a chart that educated me. 

EDIT: Just now saw a post by @p_toad. A big THANKS for that. Much more concise than the chart I found.

And, thanks to all for your replies. This is a great forum thanks to you guys.

Edited March 2, 20188 yr by Gene Howe

Gene, if you experiment with different size taps and bolts, please let us know how it went.  What worked, and what didn't, so that we can learn from your experience.

12 hours ago, PostalTom said:

Gene, if you experiment with different size taps and bolts, please let us know how it went.  What worked, and what didn't, so that we can learn from your experience.

Will do, Tom. Might be a while, though. 

I use a threaded brass insert that takes a swelling tool.

I drill the hole and then take a mill cutter and make the hole 

wider only down deep inside. Then I drop in one of the inserts

and use the swelling tool to expand it. Most of the one I use is 1/4-20.

Edited October 20, 20196 yr by Kevin Beitz

50 minutes ago, Kevin Beitz said:

use a threaded brass insert that takes a swelling tool.

I drill the hole and then take a mill cutter and make the hole 

wider only down deep inside. Then I drop in one of the inserts

and use the swelling tool to expand it. Most of the one I use is 1/4-20.

Any chance you have some pictures, sounds interesting.  Never heard of a swelling tool, but maybe have seen but didn't know what it was.

What @Woodbutcherbynight  said

Works great for both wood and metal...

 

 

Search     rivnuts    they are a threaded insert that work similar to pop rivets.

On 3/1/2018 at 1:21 PM, Gene Howe said:

Thinking about end grain...maybe some CA on the threads would toughen them up in less dense wood? 

One of the guys in the club did a presentation on this last year.  He had special taps for wood (vs. metal) but said the metal taps (coarse thread) work in a pinch.   Once cut he put in some thin CA glue, let it set up and ran the tap through again.

But T-nuts, barrel nuts, connector nuts, and threaded inserts work, too.

Edited October 20, 20196 yr by kmealy