Part of foot to move slowly (4)
I believe the answer is:
Here is my best explanation:
This clue is a double definition.
'part of foot' is the first definition.
('inch' is part of 'foot')
'move slowly' is the second definition.
(I've seen this before)
'to' is the link.
(Other definitions for inch that I've seen before include "Foot division", "0.08333 of a foot", "Islet (Scots); twenty-five.four mm", "Twenty five point four millimetres", "One point 63380 th of a mile", "Move by small amounts", "Short distance", "Short length", "Imperial measure" and "Move very slowly - a very short distance".)