Why are arris rails preferred for feather edge fencing

[barnsley7]

I'm about to make feather edge fence panels on a slope. Not stepped, I'll be having top cut parallel to ground.

Also using durapost which has 50mm gap for the rails. And using dewalt nailgun 50mm galvanised nails 2.8g ring shank.

I don't know what rails to use... I thought 38mm depth rails (a normal 3x2 inch) but I've read that arris rails are preferred? -
Is that right?

Probably going for 125 or 150mm width feather edge boards @16mm thickness 1.8m fence with durapost gravel boards and top rail.

 

[foxhole]

Arris rail does not allow rain to sit on top and rot it quickly and the shape resists warping and twisting in the weather .

 

[Diver Fred]

Arris Rails = cheapness.

Should use Cant Rails with slope at top away from boarding. If fence is over 1.2mtr high use 3 rails. Prolongs fence life with gavel boards. You can get capping for feather edge fencing. Or Local to you https://www.jtatkinson.co.uk/landsc...ng/fence-capping-38x50mm-tanalised-green-3-9m

 

[barnsley7]

thanks, that's great info.
I might also trial the durapost capping rail but not sure if it will look ok on a slope.