3/4" shaft for longer travel.
The DiMarzio 500K Long Shaft Potentiometer is designed to replace pots on guitars, such as certain Les Pauls, where the shaft needs to travel 3/4" to meet the control knob.
Here's a list on some guitars that do require a Long Shaft (3/4") Potentiometer:
Les Paul Standard, 1977-current
Les Paul Custom, 1977-current
Les Paul Deluxe, 1978-current
Les Paul Pro, 1977-1982
Les Paul Studio, All Years
Les Paul Classic (1960), All Years
Historic '68 Cus. Reiss., All Years