I liked the original heavy duty design made by thfo (http://www.thingiverse.com/thing:2045424), but it needed to be tweaked for the Anet A6. FYI I use 3mm glass on my hotbed.

Below are the changes and improvements made:

• Moved the screw hole to center it for the A6 hotbed and allow it to be tight on the edges of the bed.
• Increased the screw hole size to allow the M3 screw to slide through.
• Added a circular slot around the screw hole to keep the bed spring centered.
  (Best when used with spring washers on the bottom as well:
  http://www.thingiverse.com/thing:1895223)
• Created a home corner version to avoid the head hitting when at the home position.

I printed it in PLA since my bed never goes over 60C, but you should use a more heat resistant filament if you print in ABS, or other high heat filament.

Do NOT use the full holder on the home corner, the pre-extrusion happens directly on the holder. Use the home corner holder for the home corner.

If you have any suggestions, or improvements, let me know.

EDIT March 27 2017: I have uploaded Version 2 of the home and other corner holder. This version has a larger slot for the springs. I have not printed the new version so please comment if the slot is too large.

EDIT December 14 2017: After feedback from Peroxyde who printed both version 1 and 2 of this thing I have opted to delete version 1 since V2 fits best.