Barograph nib, individually tested Overall length almost 20mm, from nib centre to end 17mm distance between the 2 clips 13mm the nib is almost 6mm long Barograph nib, standard - (individually tested) These are the traditional type of wet ink nibs often used on old barographs. We can not be certain they fit any arm but we use them on practically all old barographs using one pen. If the arm has corroded or is just wider than normal then sometimes a new arm or some alteration to what you have may be needed. Generally a competent person should be able to open the tangs of the nib a little and slide over the arm, the nib is then clasped on using a pair of pliers carefully to close the tangs around the arm. Made from stainless steel so should last many years if not damaged. Overall total length is almost 20mm, from nib centre to end is 17mm distance between the 2 clips is 13mm, the nib is almost 6mm long - there were many types made over the years, not much choice these days. Minimum order value is £18 plus VAT - this item cannot be ordered individually - why not buy some more charts as well? Or if you have sufficient charts at present and perhaps you don't require a spare nib, you may be interested in he book 'Barographs' written a few years ago by Mr Collins now in extended 2nd edition . An informative book full of interest and details of how to care for these fine instruments.