2x 26650 to 2D cell sleeve fits a pair 26650s and uses the Adventure Sport "Shorty" tail spring.   You will need to remove the anodizing inside the tail cap of your Maglite for this kit.   This sleeve has a short brass screw and nut in the top.   If you use Keeppower protected cells you will not need the included magnetic spacers to make contact between the cells.  If you're using other flat top cells you will need a magnet between the two of them.  This kit is perfect for use with the Firefly 280 lumen, 800 lumen or the Adventure Sport 5000 lumen bulbs. Sleeve dimensions 5"L x 1.3"W.

Here is a video on how to do the conversion.

1x 26650 to 2D kit uses a singe 26650 cell and the factory Maglite tail spring, and also includes an aluminum button that snaps into the factory spring to make contact with the negative end of the 26650 battery.  The sleeve has a long brass screw inside to take up the extra space in the body.  No other parts are needed for this conversion.  This body kit is perfect for use with the Firefly 280 lumen, 800 lumen or Adventure Sport 2000 lumen bulbs.   Sleeve dimension 4.4"L x 1.3"W.

Magnets: 2pc 8mm x 2mm
These are used to make contact  between a pair of 26650 batteries if your cells are not button top and don't already make contact with each other end to end.  Most cells are magnetic on the + end however not all are.  If yours are not an alternative is to place the magnets on the top and put a dab of epoxy around the edge of them to hold in place.