The MKI grenade is made of malleable iron in a lemon shape. It is externally segmented dividing it into 40 sections, has a threaded filling hole on the bottom closed by a filling plug, and a larger threaded hole on top for the igniter mechanism. The MKI is painted black with a daub of color paint on the filling plug depending on the type of filling. It was adopted by the AEF in 1917, but because of complications with the arming of the grenade it was replaced by the MKII in Aug. 1918.
The MKII grenade initially used recovered MKI bodies. After the MKI bodies were used up the body was slightly redesigned with more taper to the body and a flat base. The MKII body is made of cast iron, externally segmented with threaded holes in both top and bottom. The biggest difference between the MKI & MKII is the fuze body and the one piece construction safety lever. The MKII is primed black and after loading took place, painted gray or a gray stripe would be added.
The MKIIa1 grenade was used in WWII, Korea, and early stages of Vietnam. It can still be found in use by third world countries. The differences between MKII & MKIIa1 grenades is the absence of the filling plug as well as the grooves proceed higher on the neck of the grenade body. Early models were painted yellow to show HE filler, but because the bright yellow stood out in battle later grenades were painted green with a yellow band around the neck.