The IAM Logo
“The design for the Machinists logo was submitted by Frank French, of Machinists Lodge 12 in Houston Texas, who was a delegate to the first Machinists Union Grand Lodge Convention held in Atlanta, Georgia in May 1889. It was chosen over several others submitted. The figures on the design are a flywheel, a friction joint caliper and machinist square. The initials of the organization are inserted between the spokes of the flywheel. The symbolism of the flywheel is significant because it generates a lot of power once it gets started. The historical connection with the trade is clear since most shops in those days were powered by stationary steam engines with large flywheels. The contemporary symbolism of the open calipers is “an invitation to all to join. The square signifies that we are square and honest.”
From Wikipedia