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Caster Stem Thread Engagement

Check how much thread a threaded-stem caster actually engages in its socket, and whether the engaged length carries the load without stripping the thread.

A threaded stem carries its load through the engaged turns, so a stem that is long enough to reach is not necessarily long enough to hold. Enter the stem diameter and pitch, the engaged length, the material, and the load, and the calculator returns the engaged turns, the shear area, and the stress the load produces.

The shear-area approximation ignores the real thread form and the bending a caster stem sees because the load is offset from the stem axis; a caster stem fails in bending more often than in pure stripping, so the result is a screening check rather than a certificate.

Inputs

Thread and engagement

Range: 0.25–1.25 in

The major diameter of the thread, for example 0.5 for a 1/2-13 stem.

Range: 4–40

1/2-13 means 13 threads per inch. Coarse threads are the norm on caster stems.

Range: 0.05–3 in

The length of the stem that sits inside the socket with thread in contact. That is the shorter of the stem thread length and the socket depth.

Load and materials

Range: 10–30,000 lbf

The tension the caster puts on the stem. On a caster carrying weight, this is roughly the load, because the stem holds the whole caster to the equipment.

Result

Engaged length / diameter
1.50
Thread stripping capacity (lbf)
23,562
Full threads engaged
9.8
Utilization of that capacity (%)
3
Verdict
The engaged thread carries this load with margin, and the joint is limited by the caster's bracket rather than by the thread.
Engagement note
Engaged length is at least one stem diameter and at least three full threads, which is the normal practical minimum for a threaded fastener.

What to check

  • Measure the engaged length in the installed position, not the stem's total thread length.
  • Check the socket boss or wall thickness, because a thin boss fails before the thread does.
  • Treat a pass as a stripping check only and inspect for stem bending separately.

Related calculators

The shear-area approximation ignores the real thread form, and a precise check needs the thread standard and its actual shear area rather than a diameter and pitch. Stem bending is not included, even though the offset load means a caster stem usually fails in bending rather than stripping. Sound, uniform socket material is assumed, and repeated loading, vibration loosening, and thread locking are not modelled.