Mounting blocks are used when it is impractical to place the penetrameter directly on object being radiographed. Most codes specify that a mounting block of the same material and thickness be placed with penetrameter, adjacent to the part, in such manner that it will show clearly on the radiograph. Standard mounting blocks are supplied in sizes corresponding with IQI sizes.
Sizes up to 2 1/2″ are 1.0″ x 2 1/4″ long
Sizes over 2 1/2″ are 1 1/4″ x 3″ long
These dimenstions allow at least 1/8″ clearance on three sides of the IQI.