Sci-Supply LC2015 Plastic D-Cell Battery Holder, Series or Parallel (Pack of 4)

why cant i get the free shipping? i only wanted 3 sets of these and i had over 35.00 worth of stuff in my cart. When I went to check out it said no

Please advise as to how two holders can be connected side by side to get 3 volts. End to end works fine. But, side by side puts both poles together

it appears the "D" positive terminal does not make good contact with the copper rivet unless i use a piece of aluminum foil as a shim. suggestions?

Can wires be soldered to the connectors?