The bolt should have a loose attached split lockwasher. Jeff's picture shows a "B" with three distinct circles and the washer's split. In my collection, I have the same head marked "B" with a single circle, "B & H" (the most quantity), "B/H", three large circles and three small circles. AMK has a picture of the "B" with a single circle in their catalog (B-12304, B-10901) but the washer appears to have serrations which would not be correct.
Jim