The joints are mortise and tenon with the mortise longer than the tenon so that the joint can shift under tension. Note the rounded aspect of the joint to facilitate movement. This is a good video on making a simple one:
You can put different blades in them; fine tooth for woodworking or coarse for rough cutting like I used. Coarse blades can be had at any hardware store. Finer blades can be had online from several sources.
