Dimensions: 1/2" od x 1/8" thick with countersunk hole for #4 screw
Tolerances: ±0.004" x ±0.004"
Material: NdFeB, Grade N52
Plating/Coating: Ni-Cu-Ni (Nickel)
Magnetization Direction: Axial (Poles on Flat Ends)
Weight: 0.0985 oz. (2.79 g)
Pull Force, Case 1: 6.52 lbs
Pull Force, Case 2: 15.06 lbs
Max Operating Temp: 176ºF (80ºC)
Brmax: 14,800 Gauss
BHmax: 52 MGOe
Strong countersunk ring magnets sized specifically for #4 flat-head screws.  The south pole is on the side of the magnet with the large hole, where the head of the screw would be.