I have some wire shelving units that I would like to extend the poles on to make them taller. The shelves are composed of two vertical poles that are female threaded on one end. The poles are connected with a connector that is male threaded on both ends. Unfortunately, the poles are only threaded on one end, so I need to find a way to put threads on the unthreaded side of other poles I have. (the photo with the green arrow shows what I am trying to thread).

I don't have any experience doing taps, and I cannot figure out how to determine the size tap I need. I found a lot of charts for various drills required for a tap, but nothing that links them to the size of the 'hole' or pipe being drilled(someone needs to create a simple calculator!). I don't even know if it is metric or not; the ads for the shelves (they are all pretty standard) say "1 inch poles" but any tap I found at 1 inch was either 8 or 12 TPI, and these are closer to 16 (or they are metric). Even more confusing, the connectors say 'coarse' thread. The connectors also are described as having a pitch of 1.5 mm.

The closest I can figure is maybe a M23x1.5? Is the diameter of the tap the same as the interior pipe dimension?

Also, if I'm tapping by hand, would a 'plug' tap be the right one to get?


enter image description here

enter image description here

enter image description here

enter image description here enter image description here enter image description here

  • Is there any chance you can get the components from the original manufacturer? My tap set has a thread guage tool (multiple blades with various thread pitches/depths) but nothing I have in the mechanics set has a tap large enough to handle that. Perhaps a contractor who installs natural gas pipes could help you out, but I have no idea how you would hold the connector material with the threads that close
    – RetiredATC
    Jun 15, 2023 at 23:10
  • Rather than complicated connectors, why not take a 2' dowel, sized snug and pinned in place with a through bolt? Jun 15, 2023 at 23:30
  • No luck on the original manufacturer, they (and other resellers) just sell the poles, and they all seem to be made the same way, threaded on only one side (even though that makes little sense from a SKU/inventory perspective).
    – bill333
    Jun 16, 2023 at 0:32
  • 1
    When they fall over or collapse in their newly extended, less stable version; and hurt someone, the manufacturer not providing double-threaded versions will be very useful to them in court proving that the liability for that is entirely on you for making unapproved modifications to their product.
    – Ecnerwal
    Jun 16, 2023 at 0:43
  • 1
    Sure seems like the easy button would be to just buy a shelving unit that comes with longer vertical struts.
    – Huesmann
    Jun 16, 2023 at 13:57

1 Answer 1


In case someone is facing a similar type problem, this was the answer:

I used a M23 x 1.5 pitch tap.In other words, the tap is the diameter of the interior of the pipe, which is 23 mm. The threads looked good, but I had a little problem getting the threaded connector started, so after some trial and error I used a slightly larger tap to make about half a thread. (It was actually a 1 inch SAE coarse 8 threads/inch, which isn't the right pitch, but it was just enough to allow the connected to engage). The connectors fit nice and snug, as did the poles.

I estimated that I saved over $500 doing this by not buying longer poles, and even more if I replaced the entire shelving units. In both cases I would have had either poles or shelves I could not use and would have had to trash them, which I hate doing.

Thanks for all who made suggestions.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.