Is your son a W-2 employee or is he an independent contractor? If he gets a W-2 for his job he cannot deduct anything for the tools on his federal tax return. Job-related deductions were eliminated from federal tax returns when the tax laws changed for 2018 and beyond. If he is an independent contractor he can enter his tools on his schedule C with his other business expenses. Does he get a W-2----or does he get a 1099NEC?
Sorry---W-2 employees cannot deduct job-related expenses on a federal return. Job-related expenses were eliminated as a federal deduction for W-2 employees by the tax laws that changed for 2018 and beyond. Your state tax laws might be different in AL, AR, CA, HI, MN, NY or PA.
https://ttlc.intuit.com/questions/4482873-which-federal-tax-deductions-have-been-suspended-by-tax-reform