tap and die set

[Enchanted Cobwebs]

I also think you could use 2.0 mm metric stainless steel bolts (they call them machine screws), with the heads cut off and matching nuts instead of tubes. They have them at Clerkenwell Screws.

I tried google but couldnt find them on line so will phone tomorrow and get a few to play with. Thanks again and also for the tip on centering though that will probably fox me too!
Thanks
Helen

[Joe]

Maybe the walls dont need to be so think to put a screw thread in?

It all comes down to a horrible table of numbers (Thread Sizes) and a rough rule of thumb, diameter should be twice hole size.

If you moved up to M2 - a cheap and commonly available size - you'd need an internal tube diameter of 1.6mm. the advisory nut diameter is twice the screw diameter, so 4mm - near enough to the 3.95 from cooksons, so you could reasonably happily drill out your little sections of tube with a 1.6mm drill, then tap them with a 2mm tap and consider them reasonably robust.

As Dennis says, silver is a very soft material for this sort of thing, so you must maintain as much material as possible by choosing sizes carefully or you'll end up with just a tiny amount of silver overlapping in the threads and it won't take long for that to wear and the screw to stop working. For the same reason, you should cut the threads carefully so as not to cut away more material than necessary.

I can't see any appropriate sizes in the Cookson white-gold range. I suppose you could work from wire and drill the hole yourself... but £28 for 1cm of 4mm doesn't sound ideal for this, even when buying minimal amounts!

Since you've got the silver tube, I'd have a go at drilling with a 1.6mm drill and tapping M2 and trying it out!

[Jelolye]

I apologize for bump the old topic, but I have some interesting observations that I would like to share, maybe this will help someone in the future because once I was on the lookout for useful advice.
or tapping holes First you must use the proper size drill,for that you referance your handy chart http://www.brokenbolt.com/images/sta...-tap-drill.pdf

For example a 1/4-20 requires a #7 drill,but you can also use a #6 or a #5 thread strength is still there and its easier on the tap,any bigger than that and you lose too much thread strength.

Drill hole straight,preferably using a mill or drill press,can be done by hand,then lube up tap making sure it stays straight and go to town,thread it in and backoff and clear chips as you go especially in a blind hole or deep thru hole.

A die is used for cutting new threads,can be used to clean up threads as well. Most tap and die sets you find around are carbon steel which arent that great(depending on the threaded material) but if you dont use them often work just fine. HSS is preferred but you will pay more best for sizes you use most,as with taps make sure to use some cutting oil.

To fix stripped threads you need Helicoil(thread repair kit) kits https://mechanicguides.com/best-tap-and-die-set/ of the proper size,they come with what you need. just dont try and use the helicoil tap also known as an STI tap to tap your regular holes or you will be hosed. Also you can redrill and retap to a larger size if possible.

Here's a vid i found on youtube for you:

[ps_bond]

All that would be great a) if we worked in Imperial that much any more over here (thankfully selecting the correct tap & drill is much easier with Metric) and b) if we wanted to repair a stripped hole in, say, an engine block (which brings in the issue of maintaining a straight hole). Doesn't really have a huge amount of relevance to jewellery.

Carbon steel taps are fine for softer metals in small section.