This adapter is for 2 D cell flashlights. This adapts a single 18650 battery to replace 2 D cells. 

Extra parts needed:
1. 1 penny for negative end
2. 4 1/8"x 52mm dowels or plastic rods
3. 5" of 14ga stranded wire

Instructions for assembly:
1. Strip back 1/2" of insulation. Push through bottom piece. Then flair out the strands. 
2. Take penny and insert into bottom of the piece. You will need a pair of plairs to seat the penny against the flaired out wire. See photo #3.
3. The top piece is two pieces. Super glue the part without holes onto the second piece. Use a battery to line up the hole for the battery.
4. Remove battery after glue has activated. 
5. Now slide wire through hole and cut the extra off. Pull wire back out and strip back 1/2" of insulation. Slide wire back through hole in top piece. Cut away any wire strands that prevent wire from laying flat in bottom of the hole. See photo #2.
6. Now super glue ends of dowls and press into top until they bottom out. 
7. Place several drops of glue on the dowel ends. Then press the bottom piece onto the dowels. Besure they are flush with the bottom of the bottom piece. 
8. Push the 18650 battery into hole on top firmly setting the battery against the flaired out wire. 
Test for continunity. 
From postive end to negative end adapter needs to be 123mm.

http://www.thingiverse.com/thing:1000572