Wrenn lodged patents on their Formula 152 range. The first being 844.436 which was quoted in the February 1961 Price List with others pending. The November 1962 Price List also listed 894.837 with still others pending. By the time of one of the last Catalogues (possibly the last one) 894.838 had also been added. Overseas Patents were stated as pending on the first Price List and not mentioned again on subsequent Price Lists although later Price Lists from November 1962 did state ‘other Patents pending’.