In the comments on yesterday’s piece about Bolt Depot’s poster of fasteners, a reader, JamesB, wrote:

I would encourage budding young fabricators to also take a look at the bolt grade charts and get an inexpensive universal thread gauge. For found fasteners, the grade markings help differentiate metric from SAE, and the thread gauge helps separate the coarse from fine. After you twist the heads off some inexpensive fasteners, the need for the higher grades becomes apparent pretty quick.

Bolt Depot has a decent printable chart (which links to a deeper database) of common bolt grades, sizes and what their head markings look like. Here’s the link to that page:

Bolt Grade Markings and Strength Chart

Know Your Bolts Redux
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