Brass roundhead pozidrive screws

[petek]

I'm making some new tee marker posts for my golf club. Posts are varnished redwood with signs screwed on indicating hole number, hole length etc. Ques tion is: what screws to use? Size of screw No3 x 1/2", or 3mm x 12mm. My th oughts are Brass for corrosion resitance, round head 'cos the holes in the signs are not really big enough to countersink but could do if necessary, P osidrive 'cos I've got nearly 300 screws to drive. BUT....I can't find any like this! So, I'm going to have to compromise on material, head shape or r ecess.

Any thoughts? I've read that stainless steel are a bit dodgy when you come to take them out as they can shear off. How does zinc passivated, or black jappaned compare to brass? Would any of the new proprietary types be worthw hile (Spax etc)?

Thanks for any advice.

Pete

[Nightjar]

Round head is not a Pozidrive head shape. The closest would be pan head. An alternative would be raised head, which are slightly countersunk and slightly rounded.

Brass may dezincify when used outdoors, so I would use either A4 stainless steel or silicon bronze. If you have worries about stainless steel shearing, which I would not expect with A4 (A2 is less corrosion resistant), use a larger diameter.

Colin Bignell

[Dave Liquorice]

+1

For flat plate signs on a post I think raised head will be best. Round or pan are going to stick up too much.

I've not had any problems with that but passivated or black japaned won't last at all:

With almost any old screw I remove outside being in that sort of condition I use brass or stainless now but see below.

I've used A2 stainless(*) for a gutter bracket they sheared off in service, large icicles probably didn't help.

(*) As that is what Toolfix sell.

[F Murtz]

Or monel?

[harryagain]

Any thoughts? I've read that stainless steel are a bit dodgy when you come to take them out as they can shear off. How does zinc passivated, or black jappaned compare to brass? Would any of the new proprietary types be worthwhile (Spax etc)?

Thanks for any advice.

Pete

You won't get brass pozidrive, the alloy is too soft. So just use slot head. Be sure to drill a pilot hole for brass.

Or stainless steel.

[Nightjar]

On 01/02/2014 09:35, harryagain wrote: ...

...

Some brass alloys are too soft, but not all:

Colin Bignell

[Nightjar]

The brass screws I used hardly lasted 20 years. However, I'm not entirely sure that using them in oak might not have contributed to the failure.

+1

Used with hot dipped galvanised gate hinges, I have found No 10 galvanised screws have lasted quite well. Not enough to reuse, but not difficult to remove.

I would always use A4, which is a marine grade aka type 316, outdoors. A2 is type 304 stainless steel, which is rust resistant, but not rust proof.

Colin Bignell

[PeterC]

mmm, I used A2 for pretty well all fastenings on bikes and trikes over the last 40 years. One trike broke irrepairably, it was left, covered in salt from the roads, in a damp sheds for 15 years and the A2 nuts and bolts came undone with no trouble. A2 is, AIUI, somewhat stronger than A4.

[Nightjar]

They have identical mechanical properties, apart from A4 being very marginally harder - Rockwell B 95 cf 92 for A2.

Colin Bignell

[PeterC]

Interesting. IIRC my info came from a supplier, so not necessarily correct.

[Dave Liquorice]

I'll have to tell the 50+ 1 1/2" No.8 brass countersunk pozidrive screws I have they don't exist then.

Agreed the alloy is soft pilot hole or correct hole for plug is essential along with a good condition driver.

[Dave Liquorice]

If they had been iron based in oak you'd have been lucky to get 2 years let alone 20... Oak is normally joined with proper joints and pegs of oak, it attacks most metals.

Hot dipped galvanised is the only decent protection method for iron/steel. Mind you galvanised screws seem to vary in quality. The similar sized ones for our gate hinges have rusted...

[Nightjar]

Mine came from Machinery's Handbook, 3" thick, despite being printed on very thin paper, and full of useful engineering information. It is usually reliable.

Colin Bignell

[PeterC]

I used to have Kempe (sp?) but didn't think to look in that. Anyway, I reckon that 15 years or so of salt is a reasonable test, especially as it would have been damp most of the time.

Actually, even the plated spokes unscrwed easily - but I always grease my nipples!