In the mid 50s the quality 24x pens were replaced by a new design, the 250 series, that featured a slip on cap instead of a screw cap and a new nib design that resembled a wing or feather.
Not everyone liked the new slip cap or the new nib even though the new wing nib was one of the most flexible nibs yet and so to hedge their bets Montblanc also released one traditional nib screw cap model, the 264.
The 264 looked very much like the discontinued 244, featured two cap bands an a very simple monotone nib, a straight section instead of the concave section on the 14x series and a plain blue ink view window unlike the striped one on the 146.
The 264 was also slightly shorter than the 146 or 256 as expected.
The 264 has withstood the test of time better than the 250 series which tend to develop cracks in the cap lip over time and the nib on my 264 is smooth and soft but without the flex found in the 146 of that period. This particular nib was changed out at sometime during its life, the imprint on the blind cap shows EF but this nib is on the fine side of medium.
In all, if you are looking for a lower cost alternative to the celluloid 14X Montblanc pens of the 50s, the 264 is an often under priced and underappreciated option.