Square nuts.
Zinc plated steel.
Standard metric coarse threads
M5x0.8mm pitch; 8mm across flats; 2.5mm thick.
M6x1mm pitch; 10mm across flats; 3mm thick.
M8x1.25mm pitch; 13mm across flats; 4mm thick.
M10x1.5mm pitch; 17mm across flats; 5mm thick.