Strap-brasses should be fitted to their straps with regard to the length-marks shown on the straps' edges. The bottom brass is first made to bear properly upon the bottom of the gap; after which, the intended face of the brass can be shown by reference to the length-marks. Whatever superfluous metal is seen beyond these marks, is the amount to be planed off or by other means cut off the brass. The other brass is next fitted down until its face touches the face of the first one. The amount of metal to be cut off the faces of both brasses, depends on their thickness, and the room to be allowed between the brasses and the rod's extremity.

If the two brasses are fitted to the right places, the two faces or surfaces which touch each other will exactly coincide with the length-marks on the strap, which indicate the centre of the entrance of the hole when bored. Consequently, each brass when bored will possess a semi-cylindrical gap, instead of one brass having a gap deeper than the other. If the required centre of the hole is not first shown on the strap previous to fitting the brasses, it may happen that the gap in one brass when bored will be an eighth or a quarter of an inch deeper than the other. This irregularity causes a large amount of filing and improper reduction of that brass having the deepest gap, in order to fit it to its spindle or crank-pin, although the hole may have been bored to the proper diameter.