The PING 4A putter was first designed in in 1959. It was a mallet putter with a sight line cast into the top. According to the first year's orders in 1959, the 1A putter was the overwhelming choice. Out of 454 confirmed orders received by PING in 1959, 427 of those orders were for the 1A. How many putters were for the 4A? Zero. [And The Putter Went...PING (2017) by Jeffery B. Ellis]. That surely goes a long way in explaining the rarity of this putter.
This is a "transitional" putter that is stamped with PING's early Scottsdale address that is lined out with PING's later Phoenix address listed below. PING moved from Scottsdale to Phoenix in mid-1966, so this putter head was likely produced while PING was still in Scottsdale, but not sold until the move to Phoenix. This putter is in excellent condition.