These are genuine MTC flat black oxide steel button contact points which can be used on any brand indicator, mechanical or digital, providing you have chosen the correct thread size.
A flat contact is normally used to measure round shapes such as spheres or rods. If it is used for flat surfaces, you will have to make sure it's parallel. The upper surface of the contact point can be used to measure overhangs, undercuts or grooves. Under other circumstances, this type of contact point can be used to measure thickness of foam, soft plastics, fabric or leather where standard contact points would tend to create impressions and result in false readings.
The disc thickness is .095" (~ 2,4 mm).