Chair screws for maintenance??

[Kris1986]

Hi,
Does anyone who works in maintenance know if the "S" on the top of the screws means standard, The "AS" means above standard obviously with a wider thread and "M" stands for maintenance screw. That is what someone told me when i first started. But now people are saying "S" and "AS" are the same thread size and "M" screws are the next size up??

Thanks Kris

 

[Howezy_21]

M is the metric diameter of a bolt. So a M6 bolt has a diameter of 6mm so it will fit in a 6mm hole. At least that's what I've learnt on my Engineering and Automotive courses. I've never heard S or AS used before

 

[Llanigraham]

M is the metric diameter of a bolt. So a M6 bolt has a diameter of 6mm so it will fit in a 6mm hole. At least that's what I've learnt on my Engineering and Automotive courses. I've never heard S or AS used before

You are looking at it from an engineering viewpoint, and thinking about nuts and bolts. A chair screw is something very different.
https://www.google.co.uk/search?hl=...0k1j0i24k1.0.bZLq3LqGDN8#imgrc=uby0smgwDeFp3M:

 

[alxndr]

Just had a look through my Ellis' British Railway Engineering Encyclopaedia and found the following entries for AS and M chairscrews, plus a few bonus ones which might be helpful:

AS Chairscrew The normal length (6 3/8") Chairscrew (or Baseplate Screw) used to secure chairs and baseplates to Wood Sleepers and Timbers. See also LS Chairscrew, LX Chairscrew, M Chairscrew.

M Chairscrew See Maintenance Chairscrew.

Maintenance Chairscrew An AS Chairscrew with slightly larger threads used as a replacement for loose and worn Chairscrews. Also M Chairscrew.

LS Chairscrew A longer (8 1/82, 206mm) version of the AS Chairscrew for use in built-up Bullhead Crossing "A" Chairs, Thick Based Baseplates and Thick Based Chairs.

LX Chairscrew A long (12", 305mm) Chairscrew used for fixing Crossing Timbers.

Maintenance Coil A helical metal liner used in worn Chairscrew holes in Wood Sleepers. Also Coil, Vortok Coil.

I note that there was no mention of, or entry for, an "S Chairscrew", but there were entries for AS1/AS2 chairs and S1/S2 chairs, which makes me wonder if S chairscrews are designed for the latter type of chairs (which seem to be of an older type based on their entry in the encyclopaedia. I might be completely off the mark there though, being an S&T bod rather than a pway one.

 

[Kris1986]

Thanks for the replies we do not actually stock "S" screws just "AS" AND "M" but a lot of track which is mainly all old bullhead does have a lot of "S" screws installed to the chairs, just seems strange and they must have been in use around 20 years ago.

 

[LukeEasta]

An AS screw is suppost to be used for new sleepers or sleepers with no rot or excessive wear. M screw is maintenance as stated above and has a thicker thread, these can be used with rotting or poor sleepers.

A S1 chair is for new 95lb bullhead rail, AS1 is for worn 95lb bullhead rail. S2 is for 85lb rail. S1J and S2j are chairs that sit either side of a joint.

A LSA screw has a long thread and is used for crossing noses. A LXA screw is even longer and I believe these can be used on longitudinal timbers.

The only chair I am still to find out is a S1M chair, this is thinner in width. All I can make out is it is a maintenance chair for indented sleepers and each chair is machined differently and thicker in depth to help with the track top.