Kind thanks to Joost from Appelboom Pennen, who lent me this Parker 51 fountain pen.  If you shop at Appelboom, use the discount code in the banner below (‘friend’) for 10% off your purchase – excluding Montblanc.

Measurements
Length (capped): 139.7 mm/5.50”
Length (uncapped): 118.2 mm/4.65”
Length (posted): 152.8 mm/6.02”
Diameter (section): 7.8 – 10.3 mm/0.31 – 0.41”
Diameter (barrel): 7.2 – 11.5 mm/0.29 – 0.45”
Weight (all): 25.5 g
Weight (cap): 13.0 g
Weight (body): 12.5 g