stress thus protecting the pad from excessive distortion and improving the pads capacity to handle heavy loads an even higher density array of studs of mixed diameters and heights is shown in fig8 in this example the wider upper studs 19 are laid out in staggered rows 20 each upper stud 19 is opposed on the lower side by a secondary stud 21 of a diameter that is less than that of the upper stud 19 surrounding each secondary stud 21 on the lower side is an encircling array of primary lower studs 22 that are offset from the upper studs 19 and are of a smaller diameter than such upper studs 19 thus the lower primary studs 22 are not opposed by a secondary stud on the upper side and the bearing area of primary studs 22 on the lower side exceeds that of the secondary studs 21 on the lower side in all of the foregoing drawings the studs whether of a round or rectilinear cross section have been shown as having vertical walls and sharp corners and edges these are not essential characteristics the corners 23 of the studs 24 at the base of the stud walls 26 may be filleted 27 for ease of manufacture and to reduce stress concentration and subsequent crack formation this is shown in fig9 studs have been shown which are round and square in cross section these shapes are not critical to the functioning of the invention.