The edges of the Ames' cross guards are slightly rounded and the space between the edges are curved outward. This creates a finial that is a bit undefined. This feature is common to most of Ames' production, excluding the very early and post war production.
The steel rivet in the center of the cross guard is a feature that most of Ames' bayonets do not have but there are exceptions.
Pre war to early war press stud and spring production
The press stud spring, normally 41 millimeters long, has been ground on the backside leaving the spring thick at the screw hole tapering to thin at the opposite end. This is similar to Harpers Ferry's springs but without as much tooling. Also notice the extra tooling around the Ames' screw hole. This feature appears to have been done on early Ames production and dropped on later production.
In the press stud assembly, there is a notched extension on the spring side of the press stud that prevents the stud cylinder from rotating in the hole drilled through the hilt. This tooled rectangular extension fits into a notch cut into the brass hilt under the spring. Harpers Ferry also started using this style of press stud at about the same time in history. Who set the standard is unknown.
Late war to post war press stud and spring production
As the war progressed, Ames simplified the production of the press stud and spring using a very similar approach to Collins & Co. These changes are first noticed with the Sharps Model 1863 bayonets. The press stud spring length was increased to 45 millimeters long and longer, but it is still thicker at the end with the screw hole.