Need help with fastener size

[Sticky]

So I need to join together 2 pieces of 6061 aluminum. Need a flush mount, so would like to tap one piece then connect them with flathead fasters. Both pieces are 1/4" thick. So is a 1/4" faster too wide? I thought I remembered reading something that the depth of the hole needs to be at least twice the diameter. Is that true?

 

[fasteddie24]

That's always been a good rule of thumb.

 

[Lyaec350]

I'd do a bunch of #8 or #10 x 1/2" flatheads rather than a single 1/4" fastener. Should look nicely if you countersink

 

[russlaferrera]

So I need to join together 2 pieces of 6061 aluminum. Need a flush mount, so would like to tap one piece then connect them with flathead fasters. Both pieces are 1/4" thick. So is a 1/4" faster too wide? I thought I remembered reading something that the depth of the hole needs to be at least twice the diameter. Is that true?

The width also would be helpful. Application?