I've had a gazillion requests for smooth head black carriage bolts over the past thirteen years and every where I turned I was told that all carriage bolts have the foundry stamp on the heads. A few years ago I managed to find a source for stainless imports with no foundry stamps & since I've never been able to locate the black oxide ones we decided to send out a batch of the ones we have to be blackened. They are back now & ready to be shipped. It's an expensive ordeal, but it's what y'all have been requesting over the years.
Sold in packs of 10 black oxide carriage bolts 3/16" x 1 1/4" with 10 black oxide kep nuts for $4.00.