The one on the right is the very early production jeep dipstick. Was also found on the Willys car engine. Used until early 42 when the second early type (left) was used for a short time starting in early 42 and ending in late 42. Ford GPW early production jeeps used the style of the left one (F marked). This type was used until sometime in late 42 when they all went to a locking style dipstick and tube.