The original side frames used on the X-Cell were one piece and made of aluminum. The frames had a bend which took them from the wider lower section to the narrow upper section. Units using this one piece bent design became known as the "Bent Frame" models.

Bent frames were used on the:
1987 - 1997 Model 1001 X-Cell 60
198x - 1997 Model 1003 X-Cell 60 Custom
1989 - 1999 Model 1008 X-Cell 30       
1989 - 1995 Model 1009 X-Cell 40

The "Stacked frame" was made up of four pieces. Upper frames and  lower frames. The frames had spacers between the upper frames and lower frames which produced the same frame width as the bent frames. This allowed full compatibility between the bent and stacked frame models. The original stacked frames were graphite and were released with the model 1004 X-Cell 60 Graphite in 1994.

Graphite stacked frames were used on all versions of the model 1004 kit. Graphite stacked frames combined with a graphite servo tray sets, were only used on the 1999 and later 1004 X-Cell 60 Graphite SE (99 Spec SE).

In 1998 an aluminum version of the stacked frame was released and used on the:

1998 Model 1001 X-Cell 60
1999 - current Model 1001 X-Cell 60 ST
1998 Model 1003 X-Cell 60 custom
1999 -2000 Model 1003 X-Cell 60 CT

In 1995 the Model 1010 X-Cell 46 Graphite was released  using a graphite "stacked frame". The frame was compatible with the 1008/1009 X-cell 30/40 kits. This frame set was made available separately in both graphite and aluminum versions as an upgrade for the earlier "Bent Frame" 30/40.

The 1008 X-cell 30 kit from 2000 on uses the stacked aluminum side frames.