The most common and most likely answer to this crossword clue is the 7 letter word CATSEYE
I've seen this crossword clue in The Times
C
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More clues leading to the result CATSEYE
Buddy explains!

The straight part
We know that "Reflective stud" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case reflective stud = catseye.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 CATSEYE mean?
CATSEYE noun- (usually in the plural) A retroreflective device placed on a road surface as a marking that can be seen even at night.
- A glass marble with elongated colourful inclusions running through its axis.
- A gemstone exhibiting chatoyancy.
- Cymophane (translucent yellow chatoyant chrysoberyl)