On November 27, 1964, Karsten Solheim applied for a design patent for the MLT model putter, though the putter had actually already been in production for 7 months. The putter had a thin face and weight concentrated behind the heel and toe. This was done because Karsten's research showed that he could give the ball topspin by placing the clubhead weight low behind the point of impact [And The Putter Went...PING (2017) by Jeffery B. Ellis].

This putter is stamped with the earliest possible stamping - Scottsdale and the zip code 85282. PING moved from Scottsdale to Phoenix in mid-1966. Meaning this early PING putter had to be produced between 1964 and mid-1966.