Although official records exist that show when sliders (vertical shanks in official terminology) were introduced in 1903, currently no record has been found dictating what length the sliders should be.
This picture shows sliders of 46mm (left), 40mm (centre) and 35mm (right). Informal studies carried out by members of the British and Commonwealth Badge Forum suggest that when sliders were introduced in 1903, the length of the slider was likely to be 46mm (from top of the bend down to the end of the slider).
In 1906 an official order was issued to shorten sliders so that they could fit into the new Forage Cap so from this time onwards, it is believed that the length of sliders was 40mm or less.
(The official order is a document in the National Archives referring to the requirement to shorten vertical shanks. Archive reference of 1906 WO359/14, p80).