Numbers using the fingers (6)
I believe the answer is:
digits
This clue is a double definition.
'numbers' is the first definition.
(digit is a kind of number)
'the fingers' is the second definition.
('digit' can be a synonym of 'finger')
'using' is the link.
(Other definitions for digits that I've seen before include "Fingers, toes and numbers" , "One to nine" , "Numbers 0 to 9" .)