Why are these so Brittle? Broke 2 in a weekend. 1 slid off a roof, other got stepped on. Bad Plastic? or just junk?

Oh no! We are so sorry for the 2 breaks... All of our composite squares are made of high quality High Impact Polystyrene, so they're as rugged as a "plastic square" can be. It sounds to us like your projects would be better served by one of our die cast solid-aluminum squares that has the design and build that *does* withstand a lot of job site wear and tear. Unless you specifically need a composite square since they're so good for materials like vinyl siding, for example), we recommend our Speed Square (model S0101) or our new Pro Square (model S0100-A). Hope that helps!