Covered under William Riordan's 1906 British patent No. 10,431, the shaft in this Sellars & Payne driver has an approximately 6" long flat section positioned a short ways above the head. This flat section is positioned substantially at right angles to the face. The flat section and its orientation were designed to provide the shaft with "maximum flexibility" at or about the point where the club balances when laid on the finger or the like."  This club balances perfectly when a finger is placed under the center of the flat section. 

Riorden referred the flat portion of the shaft as the "wrist" and termed his shaft as having a "wrist shaft pattern." By varying the length of the wrist, the amount of flexibility and firmness of the shaft could be adjusted to the players desires. The goal of this shaft design was to provide the golfer with longer and straighter shots. It sounds good in theory, but apparently the shaft did not work quite as well as hoped for in reality. Or so it would seem judging from the fact no other wrist shaft drivers are known to the auctioneer. Of course there could be other examoples out there, but not many.

Another aspect about this club is that the flat area, or wrist, is wider than the shaft above and below it. This would add to the strength of the wrist and help prevent it from breaking.  

The grip is original and the head shows little use. This is an outstanding example of this fascinating rarity.