Question

The ________ nut in which small pin is screwed in the piece adjoining the nut so that it touches one of the faces of the hexagonal nut which is sufficient to prevent its getting loose.

(a) Grooved nut

(b) Penn nut

(c) Castle nut

(d) Ring nut

The question was asked at a job interview.

My question is based upon Locking Arrangements for Nuts in portion Screw Threads & Screwed Fastening of Engineering Drawing

Answer 1

Right answer is (b) Penn nut

The explanation is: The Penn nut in which small pin is screwed in the piece adjoining the nut so that it touches one of the faces of the hexagonal nut which is sufficient to prevent its getting loose. But it becomes an obstruction if the nut is required to be tightened further through a small angle.