Screws or Bolts

[unionworkeruk]

I am having steel stringers made like the bottom half of this pic and using 35mm thick planks of wood as treads.

The metal works who are used to steel treads say I should bolt the planks to the steel plates which would mean 8 bolt heads showing through the planks on the surface or recessed.

As an alternative I could use steel washer screws from under the steel into the wood which would not be seen from above.

The stairs will not have any major traffic so I prefer the screws but am unsure of the most effective and safest. I am told washer screws with additional nylon or steel washers would be OK.. Or maybe I should use 8 bolts for each 740mm x 230mm x 35mm plank which seem a bit over the top.

Any advice or opinions ?

 

[Leofric]

Coachscrews up through the steel tread support plates into the timber treads

 

[tony1851]

The load is vertically downwards so - as Leo above - screws from underneath would be fine.

 

[unionworkeruk]

Great replies. I keep saying the weight is from the top so bolts from the top are pointless as the screws are more to keep them in place rather than to take any weight which is taken by the steel supports.

I have looked at coach bolts bit never looked for coach screws ( !) which combine the two needs for strength and being hidden from view.

Thanks a lot both Leofric and Tony1851

 

[Tigercubrider]

You could also look at grab adhesive or even silicone under the treads in addition to the screws.
More to prevent any movement of the timber (although investigate any thermal/humidity expansion needs) than actually gluing them in place. Even self adhesive foam pads might grip the wood to prevent opening up the screw holes