We are not supposed to post images, but a few pictures of stove bolts seems an appropriate reason to break the rules. The 1/4" diameter 20 thread stove bolts were typically 3/8" to 1/2" long and had rounded heads. They were used to hold side covers, timing gear covers, oil pans, and other small parts to the block and head. "Slotted head" refers to the type of screwdriver needed with that bolt-head:
[img]http://www.smithfast.com/images/is16.gif[/img]

[img]http://www.boltdepot.com/images/catalog/machine-screw-slotted-round.gif[/img]