Translation guide
An Allen key (also called a hex key or Allen wrench) is an L-shaped tool used to drive bolts and screws with hexagonal sockets. In Japanese, it is most commonly referred to by the borrowed term 六角レンチ, but several other terms exist depending on context.
The learner wants to refer to the tool itself in everyday conversation or writing.
The most common and widely understood term. 六角 means 'hexagon' and レンチ comes from 'wrench'. Suitable for most situations.
This Allen key doesn't fit.
Direct loanword from English. Recognized, especially in technical or DIY contexts, but less common than 六角レンチ.
Please tighten the screw with the Allen key.
A more technical term, literally 'hexagonal bar spanner'. Used in engineering or industrial settings. スパナ is from 'spanner'.
I bought a set of hex keys.
The learner wants to talk about a set of Allen keys or a particular size.
Many hex tools use 六角 as a prefix. For example, a hex socket is 六角ソケット, and a hex bolt is 六角ボルト. This pattern is productive and widely understood.
Pass me the 5 mm Allen key.