Per Pub 535:
Unless the uniform capitalization rules apply, amounts spent for tools used in your business are deductible expenses if the tools have a life expectancy of less than 1 year or they cost $200 or less per item or invoice.
As with all other business expenses:
To be deductible, a business expense must be both ordinary and necessary. An ordinary expense is one that is common and accepted in your industry. A necessary expense is one that is helpful and appropriate for your trade or business. An expense does not have to be indispensable to be considered necessary
