If your husband is an employee of the trucking company and is paid with a W-2, you are unable to deduct any of the tools, parts and other equipment he purchased. Prior to 2018 he would have been able to deduct these expenses in the Miscellaneous Deductions subject to 2% floor as Employee Deductions.

Under the Tax Cuts and Jobs Act the miscellaneous itemized deductions subject to the 2% floor was eliminated unless you are an Armed Forces reservist, a qualified performing artist, a fee-basis state or local government official, or an employee with impairment-related work expenses. 

Due to the elimination of miscellaneous itemized deductions subject to the 2% floor, employees who do not fit into one of the listed categories cannot deduct employee business expenses.

If your husband is paid with a 1099-Misc as a contract employee, he would report the income through the self-employment section. He would also then would be able to deduct the purchase of tools, parts, and other equipment in this section.