Longest combination square?

[Deleted member 174758]

You might need to modify your thinking.

I fully agree with @^woody^ - you may need to alter your thinking. The longest off the shelf combi squares I know of are the 24in/600mm ones made to engineering standards, e.g. Starret, Moore & Wright, etc. These are pretty accurate, but at £200 a pop they are pricey. Next best is a medium quality general square such as the Bahco yer man mentions in his post. You can get a 600mm (metric) rule for these from
Axminster - I got a similar rule from a guy on eBay a few years ago - but I have never seen a rule longer than 600mm. Why would you, though? At 600mm you are pushing the limits of accuracy of the Bahco and are well beyond the accuracy of the cheap, lightweight Chinese tat so many people mistakenly buy (see example above, also note Woody's explanation for this)

If you really need a longer square get yourself a dryliner's T-square. These are metric graduated only (because plasterboard comes in metric sizes) but are 1200mm (nearly 4ft) long to the tip. I often find mine (Marshalltown) to be handy for setting out sheet materials, but super accurate it isn't (although why would it be? A few millimetres gap in a joint will just disappear when the plasterboard is scrimmed and skimmed or taped and jointed). So OK for doing floor overboarding, etc

 

[Deleted member 174758]

If you really need a longer square get yourself a dryliner's T-square. These are metric graduated only (because plasterboard comes in metric sizes) but are 1200mm (nearly 4ft) long to the tip.

Just to clarify, here is a ppicture of the 1200mm dryliner's T square being used to mark out an 8 x 4ft (2440 x 1220mm) sheet of 6mm plywood being used for floor over cladding. Big enough and accurate enough for the task

Against a combi square these are huge, but the accuracy is really only moderate