Bows can be spanned by hand up to about 160lb, heavier than this and a spanning device is usually required.
I make a full range of spanning devices and usually supply them with a bow. In all cases the devices are made to be as authentic as possible, so if you want to strip a Cranequin in front of a crowd, you will find the inside as correct as the outside.
The approximate cost for each device is given below; the bow is extra to this.

• Spanning belts can handle up to about 250lb and date from about 1200-1500 - £120.
• Goats foot levers can handle up to about 300lb and date from about 1250-1600 - £160.
• Cranequins can handle up to about 550lb and date from about 1450-1750 - £950.
• Windlass can handle up to about 1200lb and date from about 1350-1900 - £900.