McMaster-Carr: http://www.mcmaster.com/#i-beam-pipe-clamps/=my5wht

• I disassembled clamp into 2 constituent parts.
  
  
• Flange clamp was cut down to make shallow "U-shape" which becomes a kind of retro holder for my toggle switch. 
  
  
• Purchased a universal ON/OFF Toggle switch from Advance Auto Parts - the kind with flush bottom, enclosed base, no protruding wiring tabs or screws - I Iiked the more retro one with "ON/OFF" label in red and black - $2.
  
  
• The Bolt and Nut close conduit clamp for ¾” EMT or ¾” OD pipe [aka #1 size] from your I-Beam set now becomes a perfect clamp to the handlebars.
  
  
• The threaded hole at the side of the flange clamp becomes bottom of your cut down holder and bolts to the top of conduit/handlebar clamp via the supplied / ¼” -20 bolt (recycle, reuse).
  
  
• The 1/4-20 bolt is cut and ground short to sit flush inside holder; it will be secured by threading and trapped by epoxy set switch sitting above it.
  
  
• Assemble holder and clamp setup - remember to orient them at the angle you want your switch to read when on the handlebars - my location was pretty much 90 degrees to each other.
  
  
• Use JB Weld 2-Part Cold Weld Epoxy ($6) to epoxy set universal ON/OFF toggle switch into holder.  Use enough to fill the bowl of your holder, but not too much - just enough and the black epoxy will blend with the black casing of the switch to give it that - "it was supposed to be that way" look.  Interestingly enough albeit not visible in the photo - my switch was labeled "CHINA" in white letters readable above the epoxy - how appropriate!

• I purchased a 2" round, black face voltmeter by Equus from JC Whitney - $36.
  
  
• Mount voltmeter to a second Bolt and Nut close conduit clamp via supplied plastic bracket and stud/nuts/washers on bottom of meter.
  
  
• I added a stainless steel flat cable "zip" tie at top (Home Depot - 10pk - $5) to encircle bezel of meter and provide upper support to plastic holder arms.
  
  
• Attach both meter and switch units to handlebars via your clamps.  Clamps are threaded 1/4-20 pan heads but I added washers and nylon insert lock nut on the back side for safety.

• Wire as appropriate.  I ran a "+" homerun back to my battery in the trunk so I could read at will, not going thru known to be troublesome ignition setup in headlamp, and grounded assemblies to new bright metal clamps at handlebars.
  
  
• Viola!