The pic above shows an NOS Decker transmission shift lever lock for a 1935 Ford. A similar unit was also made to fit the 1932-34 shift tower.
This is a highly engineered and rather complicated device which has multiple pieces which are attached to the shift tower casting in place of the screw cap, and over the lever.
In the unlocked position, the lever is allowed to travel fore-aft and side to side as required to shift gears. In the locked condition, the lever is fixed relative to the casting and the car cannot be shifted between gears.
This pic shows the original packaging of this NOS unit.
The original instructions for installation and operation.
This view above shows the beautiful design and construction of this unit. Chrome plated moving parts, and wrinkle painted machined steel castings, topped with a classy data plate!
The view above shows the Ace lock used to operate the unit. I suspect this was a very early application for Ace locks.
This is the machined steel casting which is secured to the shift tower casting. The upper portion of the Decker lock engages the pin hole after it is screwed onto the tower casting in place of the original shift lever cap.
Here is a view showing the upper portion of the lock and how it engages both the lower portion and the shift tower casting.
After the unit is assembled, the little chrome plug is driven into the access hole, and that prevents the unit from being unscrewed or removed from the shift tower casting.
Also note the keys for the Ace lock. These are original Ace keys, and have an art deco style head in keeping with the era. I have never seen any other art deco style Ace keys!