When Gilbert made major changes in the US Meccano line, he added a series of building block sets. These were perhaps based on the Richter Anchor Stone blocks, which Gilbert had purchased in 1919. Shortly after the purchase, Gilbert continued producing the stone blocks. The series of Meccano Blocks, however, were made of a hard plastic and seem to be based on multiples of one inch (the Richter stone blocks were based on multiples of 25 millimeters for the Large Caliber stones). Four sizes were made: 201, 203, 205 and 210. This is a 201 set, with a photocopy manual.