Determining the Stem Size

Measuring Round Caster Stems
Determining the size (diameter) of your caster stem, while difficult, is critical to avoid ordering and receiving the wrong casters. Take a look at the tips on this page for help in confirming the stem size that you need.
Near the end of this page is a listing of the more common threaded stem sizes. Once you have determined the diameter and threads-per-inch (TPI) of your caster stem, you can confirm it with the listing.

Calipers may be the best method to accurately measure the stem diameter. While you may not have any calipers, here's a perfect excuse to buy some. They are inexpensive and you'll use them more than you think.
An open-ended wrench can determine the stem size.
Grip neck stems will typically be 5/16" while grip ring stems will typically be 7/16" or 3/8".
adjustable wrench
Tighten an adjustable wrench onto the stem until just touching. Then, remove the wrench and use a ruler or tape measure to measure the distance between the wrench jaws.
Take a narrow strip of paper and wind it around the stem. Make a pencil mark exactly at the spot where the paper makes a full circle. Remove the paper and measure from the end to the pencil mark.
  • If it measures just over 3/4" long, the stem is 1/4" diameter.
  • If it measures just under 1" long, the stem is 5/16" diameter.
  • If it measures 1-3/16" long, the stem is 3/8" diameter.
  • If it measures 1-3/8" long, the stem is 7/16" diameter.
  • For threaded stems, consider using your local hardware. In the nuts and bolts aisle, find a nut that easily screws onto the caster. The label on the bin from which you selected the nut will tell you the size of the threaded stem.
    Common threaded stem sizes:
  • 1/4" - 20 TPI (threads per inch)
  • 5/16" - 18 TPI
  • 3/8" - 16 TPI
  • 3/8" - 24 TPI (fine thread)
  • 7/16" - 14 TPI (this is rare on casters)
  • 1/2" - 13 TPI
  • 1/2" - 20 TPI (fine thread - rather uncommon)
  • 5/8" - 11 TPI
  • 3/4" - 11 TPI

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