The most common and most likely answer to this crossword clue is the 3 letter word FIN
I've seen this crossword clue in The Times
F
I
N
More clues leading to the result FIN
Buddy explains!

The straight part
We know that "stability device" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case stability device = fin.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does FIN mean?
FIN noun- One of the appendages of a fish, used to propel itself and to manoeuvre/maneuver.
- A similar appendage of a cetacean or other marine animal.
- A thin, rigid component of an aircraft, extending from the fuselage and used to stabilise and steer the aircraft.
- A similar structure on the tail of a bomb, used to help keep it on course.
- A hairstyle, resembling the fin of a fish, in which the hair is combed and set into a vertical ridge along the top of the head from about the crown to the forehead.
- A device worn by divers and swimmers on their feet.
- An extending part on a surface of a radiator, engine, heatsink, etc., used to facilitate cooling.
- A sharp raised edge (generally in concrete) capable of damaging a roof membrane or vapor retarder.
- To cut the fins from a fish, shark, etc.
- (Of a fish) to swim with the dorsal fin above the surface of the water.
- To swim in the manner of a fish.
- To provide (a motor vehicle etc) with fins.
- (formerly Australia) a five-pound (£5) note; the sum of five pounds.
- A five-dollar bill; the sum of five dollars.