80mm decking post into a 75mm metal post holder

Question

It appears posts designed for balustrades are 80mm wide whereas fence posts are only 75mm. The problem being is wedge-grip post holders are made for 75mm posts.

Firstly I wonder:

1. Why are fence posts and decking posts different widths?
2. Can I use a 75mm fence post for my balustrade?
3. Is there an easy, and effective way to remove 2.5mm from each side (up to the height of the post holder so it'll fit in neatly.

Or:

1. Are there alternative ways to a metpost to hold an 80mm timber post upright safely - on a concrete platform with a 1m drop on the otherside?

Answer 1

It's assumed that deck posts are being affixed to a wood base, usually the support structure beneath the deck, not concrete, so they're not sized according to wedge grips or metposts. I can't see why you can't use a fence post instead, although, given there's a drop, I'd probably go for 100mm fence post with a 100mm bolt down wedge grip holder, which you can get, just to make it stronger, but that's up to you. This only works if you don't want a slotted version of the deck post to insert supports for the balustrade string though.