Square galvanised steel ridge bars are square profile steel tubes for greater strength. Square Ridge Poles span across the centre of a tarpaulin to create a centre ridge and prevent the centre of the tarp from sagging. The ends of the square ridge pole have drilled holes so that they can fit over a tent pole spigot. A 3 piece ridge pole is made up of 2 pieces of 25mm square tube and one 22mm square tube that slides inside both 25mm tube ends this makes for a strong well supported joint. We recommend that square ridge poles over 15ft are used with a centre support pole or ridge bar helper for support and to reduce sagging. These two items are sold separately.