There is no universally valid description of the layout of piston-filler pens; mechanisms and threads vary considerably between manufacturers, and special tools such as pliers, pullers and wrenches are often needed for disassembly. On the Montblanc 31, the section can be unscrewed and replaced as a unit; the rear piston part can also be swapped out completely, which is normally safer than full disassembly. On older pre-war Montblanc models the feed and nib are friction-fit and can be carefully pulled out from the front; a replacement nib must match the feed in curvature, width and length. Tools are available, among others, from Tom Westerich (penboard.de); repair workshops at the Hamburg pen show and collector meet-ups offer a chance to learn from professionals. Beginners should first practise on cheap sacrificial pens.