Are timber bolts installed with a washer under the head of the bolt?
Timber bolts, also referred to as economy bolts in the Pacific Northwest, are designed with a round oversized head which eliminates the need for a washer underneath the head. The underside of the head has two nubs which bite into wood and prevent the head from spinning in the timber. The nubs under the head require a wood bearing surface to bite into, making a steel washer impossible to place in that location.
Timber bolts are commonly used in marine application where the low-profile head creates a safer surface than that of a hex head if a boat or vessel where to collide with the head of the bolt. The name economy bolt is used for these parts because the large oversized head eliminates the need for an expensive malleable iron, ogee, or plate washer.