These circular coupons are most commonly used with holders that mount the coupon flush with the interior of the pipe or vessel. They have a chamfered hole which permits recessed mounting with a stainless steel flathead screw. Flush disc coupons are most frequently used where pigging would otherwise require the removal of intrusive-type coupon assemblies prior to the pigging operation; or alternatively where water-drop out in the bottom of horizontal pipe runs gives rise to corrosion problems. The disc coupon diameter is 31.8mm with a thickness of 3.2mm. The insulation and mounting screw is provided with the coupon holder.