In 1936, Parker introduced a slender version of the Oversize, commonly referred to as the Senior Lockdown or Slender Oversize.
The last known date codes for uneven-ringed Seniors are from the first quarter of 1937.
There are examples of later transitional Slender Oversizes with ordinary (even) cap rings.
One theory suggests a Standard cap on a Senior body. However, documented fourth-quarter 1937 date codes indicate that some genuine late Lockdown Seniors existed.
The Vacumatic world is full of anomalies — and this model is one of the most discussed.
From top: Senior, Slender Oversize, Standard. Note the slimmer features of the two upper bodies.
With the introduction of the Speedline filler, the Slender Oversize was replaced by the Slender Maxima , which was produced only during the second and third quarters of 1937 with the raised “VACUMATIC” band.