The Coachmaker’s Jigger is also called a Side Router and was used to create a groove along a curved surface.
For an explanation of the jigger, I will use R.A.Salaman’s ‘Dictionary of Woodworking Tools’ as my reference.
The cutters are parallel to the sole, and carried in a metal housing. The single-iron type has two hooked cutting edges fixed with two screws; the double iron (London pattern) has two separate plain cutters set at 45o, secured with thin metal wedges. Used for cutting glazing or panel grooves in frames and pillars. It began to replace the Pistol Router in the mid nineteenth century.
R.A.Salaman Dictionary of Woodworking Tools, c1700-1970 Revised Edition, (1997), Astragal Press
My router was made by John Moseley & Sons sometime late in the 19th century, or possibly in the 1st decade of the 20th century.
From Salaman’s description, it is the so-called ‘single iron’ type. This is despite it actually having a hooked iron on each side.