Cutting deal, regularly handle hard stuff (6)
I believe the answer is:
enamel
'hard stuff' is the definition.
(I've seen this before)
'cutting deal regularly handle' is the wordplay.
'cutting' indicates putting letters inside (some letters cut their way into a word).
'regularly' means one should take alternating letters (regularly take one letter, leave next etc.).
'handle' becomes 'name' (handle can mean a name or nickname).
The alternate letters of 'deal' are 'el'.
'el' placed around 'name' is 'ENAMEL'.
(Other definitions for enamel that I've seen before include "Crown Protector?" , "Glassy coating" , "Shiny layer on surface" , "Decorative or protective covering on metal or glass." , "Hard substance covering teeth" .)