Same sort of ridge (4)
I believe the answer is:
seam
'ridge' is the definition.
(I've seen this in another clue)
'same sort' is the wordplay.
'sort' indicates an anagram.
'same' is an anagram of 'SEAM'.
'of' is the link.
(Other definitions for seam that I've seen before include "Join - thin layer" , "Join in knitted garment" , "Sewing join" , "Unfasten" , "Joint between two edges" .)