A Montblanc fountain pen measuring about 12.5 centimetres without its cap is as a rule a Meisterstück 146, which Montblanc sells under the name LeGrand. Capped, the model comes to around 14.5 centimetres. Since catalogue and dealer figures almost always quote the closed length only, a pen without its cap has to be identified from the length of the barrel, the diameter, the ink window and the piston knob.
For comparison: the 149 is markedly larger in both dimensions and has a noticeably thicker barrel, while the Classique 145 is clearly slimmer and shorter. The number and width of the cap rings and the lettering on the nib give further clues.
If a replacement cap is being sought, identifying the model exactly is crucial, since the caps of the different sizes are not interchangeable: threads, diameters and ring widths all differ. Replacement caps can be had through the Montblanc service department and from dealers specialising in old writing instruments, though for the older years of manufacture not always at short notice.