Let’s have a look at the Franklin-Christoph Model 66 Pocket fountain pen.

Measurements
Length (capped): 129.4 mm/5.10″
Length (uncapped): 123.0 mm/4.84″
Length (posted): 142.3/5.60″
Diameter (section): 10.4 – 12.6 mm/0.41″ – 0.50″
Diameter (barrel): 8.3 – 14.0 mm/0.33 – 0.55″
Weight (all): 14.5 g
Weight (cap): 12 g
Weight (body): 2.5 g