I used trailer floor board screws 1/4” 20 tpi with a t-30 torx head. These are the same screws used to put the floors down on semi trailers. Requires pre-drilling 7/32. I bought them on ebay various lengths as needed. My electric impact was my friend. Here is a fee-bay listing 161441454055. I am not affiliated with the seller. I did buy from him and it was good quality. The TEK from home depot look good too.
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