The crane device that limits the angle of the boom at its highest position is the boom stop (often implemented as a boom angle limiter or limit switch).

Quick Scoop: What it does

  • The boom stop/boom angle limiter prevents the operator from raising the boom beyond a preset safe maximum angle.
  • When that angle is reached, the device either stops further “boom up” motion or triggers an alarm and automatically cuts out the boom‑up function.
  • This protects against tipping, boom structural damage, and overload conditions when the boom is too steep.

How it works (in simple terms)

  • A sensor or limit switch monitors the boom angle continuously.
  • As the boom approaches the maximum allowed angle, an early warning (alarm) is usually given a few degrees before the true limit.
  • At the limit, the control system blocks any further upward motion while still allowing safe movements like lowering the boom.

Related terminology you might see

  • Boom stop (common training/quiz answer to “what limits the angle at its highest position?”).
  • Boom angle limiter / boom angle limit switch (technical description for the same function).
  • Part of the Load Moment Indicator (LMI) or luffing limit device on some cranes, where boom angle is monitored and restricted as part of an integrated safety system.

TL;DR:
The device that limits the boom at its highest position is the boom stop (boom angle limiter/limit switch), which automatically prevents the boom from being raised past a safe maximum angle.

Information gathered from public forums or data available on the internet and portrayed here.