Actually it has many paralell menings, but one of the is an angle of 53 degrees. This angle is inside a 3-4-5 triangle, where the side 3 and 5 meet. This is a part of Pythagoras ancient formula.
So this must be one of several things Orffyreus means by pointing to 5 and 3. The 3-4-5 triangle and the angle of 53 degrees.
So we can see that mechanical parts in the picture and the geometry in the number 3 itself, all substantiate a Pythagorean 3-4-5 triangle, and the number 53 is placed just where the angle would be 53 degrees, and where the sides 5 and3 meets! This is ancient masonry at it's finest. These are the methods that was used by the Rosicrucians, and the methods found in Shakespeare 100 years earlier. There is a special reason for doing this. It is really not about the triangle, but the secret figure that it supports. The ancient secret, originating way back from the ancient mysteryschools.
But has it anything to do with Orffyreus' secret invention?