You create a shim when parts of your armour are too small to fit around you. Problem areas are the calves, thighs, forearms and biceps. In the guide below I have used Industrial velcro on both sides, you can glue one side and just use Industrial velcro on the other. I use Industrial velcro on both sides as it's strong and isn't permanent, great if you need to sell your Armor later.

Step 1

 

• Cut a piece of plastic (ABS or Styrene) to the length and width of the gap you wish to hide.
• Cut 2 strips of Industrial velcro hook and super glue these to the strip of white plastic

Step 2

• Cut 2 strips of Industrial velcro loop and super glue these to back inside of the calve, where it opens up.
  

Step 3

• Place the shim you created in step 1 into clam shell. Depending on what plastic you used for the shim, you may want to heat the plastic, so it bends around you leg for a better fit.
• Now all you need to do is open one side of the shim to wear your Calve piece, this will work on other parts too.