What is the purpose of the steel nubs or fins on timber bolt heads?

timber-bolts

Timber bolts, also referred to as economy bolts in the Pacific Northwest, are designed with two nubs on the underside of the head which bite into wood and prevent the head from spinning in the timber during nut assembly.   The nubs under the head require a wood bearing surface to bite into, making a steel bearing surface incompatible with a timber bolt head.

Timber Bolts on Steel

Timber bolts can be custom manufactured without nubs underneath the head of the bolt.  It is important to order timber bolts without steel nubs under the head when the bolt head is bearing down on steel instead of wood.  The steel nubs under the head are formed during the hot-forging process when the bolt head is created.  If Portland Bolt is instructed to create a timber bolt with no nubs by the customer at the time of purchase, we are able to instruct our machine operators to forge a timber bolt without nubs.

Timber Drive Spikes

Timber spikes are designed like large nails to pin wooden members together.  The timber bolt head on the drive spike provides a large bearing surface which prevents the bolt from pulling into the wood. Since timber drive spikes have fettered lag thread they are driven into wood as opposed to having machine thread that accepts a nut.  For this reason, timber drive spikes do not require steel nubs under the head since there is no nut assembly which would cause the heads to turn during installation.

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