A series of USB based pendants for Mach3 are available.
Product pictures and manuals are in www.vistacnc.com
--- Plug 'n Play! No USB driver installation. No Mach3 configuration.
--- Work with parallel port output controller and USB based controllers like
--- 100 steps (clicks) per turn MPG.
--- Dedicated control buttons, water proof and dust tight, isolated relay
control loop, ...