1. cast from high strength,highly conductive copper alloy. 2.for connecting or protecting the ground rod. The model of connectors we supply.Item No.Internal SizeLength (mm) GRDC12M1470GRDC14M16 . 5/8’’70GRDC16M1870GRDC173/4’’70GRDC18M2070GRDC20M2270GRDC22M2470GRDC25M2770The model of coupler,clamps,diving heads,studs we reply;Item No.Internal Size GRD121/2 GRD585/8 GRDC343/4 GRDC881