Best screw/bolt for joining 4"*4" posts?

I've got a bunch of old 4x4" fenceposts that I'm going to build up to make the walls of some raised beds. Probably put an internal corner post in and screw/bolt the posts to it from the inside so that screw/bolt heads are hidden.
Any recommendations for coach bolts or screws that will get a really good "bite"? Looking for something 6-7" long.
Tim
--
Please don't feed the trolls

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Selection of coach screws at S'fix. I use an impact driver....
--
Tim Lamb

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Tim+ expressed precisely :

I am inclined to suggest threaded rod and nuts, at each corner. Posts laid so the interlink/ cross alternately at the corners, then a hole drilled through each post end, so rod can slide through where the posts meet. So your rod needs to be the full height, with a nut and washer at each end of the rod. Tighten it up with the corner square and it will not budge. You could use the same rod process, for a joint midway along a side.
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I used these to construct a framework for a gate absolutely brilliant extre mely easy to drive in with an impact driver no pilot holes and with excelle nt grip even in end grain. The screw even pulled the head into the timber s o no protrusions. The people who manufactured my timber garage used the sam e type of screw.
https://www.screwfix.com/p/timbascrew-flange-timber-screws-gold-6-7-x-150mm -50-pack/4613j
The gate
https://www.dropbox.com/s/cs489yz4mj5c4ku/2018-08-27%2012.29.13.jpg?dl=0
Richard
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Cheers. That looks like the business.
Tim
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Used 'em today. Effing brilliant things.
Tim
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On 21/02/2019 17:45, Tim+ wrote:

Anything here + impact driver https://www.toolstation.com/search?q0mm%20screws
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Dave
The Medway Handyman
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On Thu, 21 Feb 2019 17:45:24 +0000 (GMT)

Rather than a corner post, lay them so the ends are alternately overlapping in the corners, and screw each one down to the two below it.
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