I see. I did read about the Rockler class and should have made the connection they were the source of the hardware as well, sorry.
Yes, a 1/4"x20 thread would be best with an insert. I'd like to make a magnifier for a present.
Hey, have you looked at the Niles SS Bottlestopper site?
https://nilesbottlestoppers.com/
When Ruth designed her's she went with a larger 3/8"x16 threaded shaft. She has a bunch of different hardware under "Shop" but I they don't carry magnifiers so I guess it's off to Rockler!
(I see Amazon carries a lot of Rockler items but not the magnifier.)
I do have some brass inserts for the 3/8" thread, but mostly use them for making things that needs to be removed, perhaps for cleaning, such as ice cream scoops or meat tenderizers.
Meat tenderizers with dogwood handles
I find that for most woods, I can tap 3/8" threads directly into the wood and don't need the insert.
If the wood is a bit soft, I drill a slightly undersized hole and reinforce the wood inside with a bit of thin CA glue, then re-drill if necessary and then tap.
For things that never need to be unscrewed, I just epoxy the thread directly into the wood. Epoxying a threaded shaft into an unthreaded hole works fine.
On the Niles site they do sell the mandrels, but do describe one way to make a mandrel yourself, at the bottom of this page:
https://nilesbottlestoppers.com/bottle-stopper/
I like the mandrels threaded to fit the lathe spindle.
When tapping into wood (or even metal for that matter), one thing I find really helps is an inexpensive tool called a tapping guide. Available from several places but I got a couple from here:
Tap Holders & Guides 6294 Spring loaded; 3/16" diameter pin; 1/2" knurled shank; Adjustable spring; This tap guide helps you start threaded holes stra...
littlemachineshop.com
This has a reversable spring-loaded shaft that works with both pointed or conical recessed end taps.
Mount in a drill chuck in the tailstock and use the spring-loaded shaft to keep the tap perfectly straight while tapping! Works so well!
In case you are interested, here are a few stoppers I've made using the Ruth Niles hardware.
This is how I often turn the bottle stoppers. mandrel not absolutely necessary for this but better if I want to turn detail into the top.
When you turn some wooden rings, maybe share the way you hold them and such. Lots of people might be interested.
JKJ