The first 2 years of Decepticon jets (often referred to as the Seeker Jets) are some of the most confusing Transformers to properly piece together, because there are so many parts variations. To some folks, some of these variations are insignifigant, to others it is very important, but it would be impossible for me to list every possible variation out there fo every piece, so if there is a specific variation you are interested in, please ask. I have listed below some of the main variations with pictures, and a brief description to help. I am sure there are some other variations out there not shown (some are sticker related), but these are the most common. This may help you, or make it even more confusing for you. Again, I always encourage you to email me with questions. Worst case scenario, you can ship me what you have, and I can figure out what you need.

COMMON VARIATIONS
There are 2 different size pegs on the Thundercracker, Skywarp, and Starscream main wings. There is a long peg, and a short peg, and this variation is very obvious when seen side by side. However, in addition to the different sizes, there is also a flat peg, and a beveled(rounded) peg for both the long peg, and short peg. However this doesn't show up very well in a picture, so I didn't bother. So that brings to total 4 different pegs (long beveled, long flat, short beveled, short flat) available on the main wings.***Please note that sometimes people will "cut" the large pegs to make them match a short peg wing they already have.
For Starscream, Skywarp, and Thundercracker, there is also another variation in the main wing, and that is that some have a slot along the inside edge of the wing on the bottom side, and the other version is completely solid. So far I have only seen the solid wing with the short flat peg, but that doesn't mean it doesn't exist with the other version pegs. The slotted version comes with all variations of pegs.
The Thrust and Dirge wings also have a variation in the main wings, There is one with a slot halfway down the inside edge on the underside of the wing, and the other version has the slot that runs almost the entire length of the wing. The short version seems to be much more common.
TAILFINS!!!!! Yes, this is probably the most frustrating part of putting together one of these jets. There are 2 different size pegs on the tailfins of Starscream, Thundercracker, and Skywarp. There is a small peg and a large peg. Of course there are also corresponding tail rudders with large holes, and small holes. The main problem is that it is near impossible to tell the difference from just looking at them, as to which size peg it has. If you put a small pegged tailfin into a large peg tail rudder, it falls out. If you put a large peg tail fin into a small peg rudder, you really have to force it in, often time resulting in cracking the tail rudder, or breaking the peg off the tailfin when trying to remove it from the rudder. The only way to really tell is if you have a set of each, and you can figure it out. I usually recommend sending me what you have when trying to select a fin, or rudder. These parts are the ones most often incorrectly ordered.
HOLLOW vs. SOLID....There is another variation among the tailfins, and that is that some are "hollow", and some are "solid". The "hollow" tailfins can have either size peg. The "solid" pegs that I have come acoss have all been small pegged versions, so that may help you out.
RUDDERS!!!...There is one way to identify which size peg you need based on your rudder without having tailfins. There is one rudder version that has a small mold mark on the bottom edge of the rudder. Do not confuse the line from the mold with the spot where the rudder was attached to the plastic sprue...sometimes the line is very close to this area, and they are sometimes confused for each other. This mold line is very hard to see, but it is parallel with the peg that goes into the jet, and perpendicular to the mold seam line that runs the entire length of bottom of the rudder. In the picture, I highlited where it will be with a black mark. Not all rudders have this mold line, but if yours does have it, then most likely it will be the small pegged version. However, the rudders that do not have the mold line, can be either large or small pegged versions, but about 90% of the ones I have seen (and I have seen a lot) WITHOUT the mold line are large peg versions..
There is 2 different versions of the launchers for Thrust, Skywarp, Thundercracker, and Starscream. Again, this one is very subtle, and does not show up well in a picture. One version has a beveled (rounded) peg tip where it fits into the jet, the other version has a flat peg tip.
In addition to the main difference in fists (single tab vs. double tab), there is also another difference. The difference is actually on the inside of the fist, and it relates to the openings created from the molding process. It is easier to see what I am talking about by looking at the picture. There are at least 4 different internal molding variations...small circle..large circle...square...rectangle. So far, I have only seen the small circle, and rectangle variations on single tabbed fists. The large circle, and square can be found on both single, and double tabbed fist.
SEEKER JETS INTERCHANGABLE PARTS
landing gear1 in stock$6
Dirge,Thrust,Ramjet,TC black fist-LEFT-double tabbed 5 in stock$6
Dirge,Thrust,Ramjet,TC black fist-RIGHT-double tabbed 3 in stock$6
Dirge,Thrust,Ramjet,TC black fist-LEFT-single tabbed 1 in stock$6
Dirge,Thrust,Ramjet,TC black fist-RIGHT-single tabbed 0 in stock$6
STARSCREAM
LEFT fist-double tabbed2 in stock$5
RIGHT fist-double tabbed2 in stock$5
LEFT fist-single tabbed2 in stock$5
RIGHT fist-single tabbed2 in stock$5
missile launcher4 in stock$2
long missile2 in stock$10
short missile2 in stock$7
large left wing with stickers-emblems -large peg0 in stock$6
large left wing no/worn stickers- large peg0 in stock$4
large left wing with stickers-emblems -small peg0 in stock$6
large left wing no/worn stickers-small peg0 in stock$4
large right wing with stickers-emblems -large peg1 in stock$6
large right wing no/worn stickers-large peg0 in stock$4
large right wing with stickers-emblems -small peg1 in stock$6
large right wing no/worn stickers-small peg0 in stock$4
blue tail rudder-left-stickers-large peg1 in stock$5
blue tail rudder-left-worn/no stickers-large peg1 in stock$4
blue tail rudder-left-stickers-small peg0 in stock$5
blue tail rudder-left-worn/no stickers-small peg1 in stock$4
blue tail rudder-right-stickers-large peg1 in stock$3
blue tail rudder-right-worn/no stickers-large peg2 in stock$4
blue tail rudder-right-stickers-small peg1 in stock$5
blue tail rudder-right-worn/np stickers-small peg0 in stock$4
grey tailfin-left-large peg0 in stock$8
grey tailfin-left-small peg0 in stock$8
grey tailfin-right-large peg1 in stock$8
grey tailfin-right-small peg0 in stock$8
SKYWARP
LEFT fist-double tabbed1 in stock$6
RIGHT fist-double tabbed1 in stock$6
LEFT fist-single tabbed1 in stock$6
RIGHT fist-single tabbed1 in stock$6
missile launcher4 in stock$4
long missile0 in stock$10
short missile0 in stock$7
large left wing with stickers-emblems -large peg0 in stock$6
large left wing no/worn stickers-large peg1 in stock$4
large left wing with stickers-emblems -small peg0 in stock$6
large left wing no/worn stickers-small peg2 in stock$4
large right wing with stickers-emblems -large peg0 in stock$6
large right wing no/worn stickers-no/worn emblems-large peg2 in stock$4
large right wing with stickers-emblems -small peg0 in stock$6
large right wing no/worn stickers-small peg2 in stock$4
purple tail rudder-left-stickers-large peg3 in stock$5
purple tail rudder-left-worn/no stickers-large peg1 in stock$4
purple tail rudder-left-stickers-small peg1 in stock$5
purple tail rudder-left-worn/no stickers-small peg0 in stock$4
purple tail rudder-right-stickers-large peg4 in stock$5
purple tail rudder-right-worn/no stickers-large peg0 in stock$4
purple tail rudder-right-stickers-small peg1 in stock$5
purple tail rudder-right-worn/no stickers-small peg1 in stock$4
black tailfin-left-large peg3 in stock$8
black tailfin-left-small peg2 in stock$8
black tailfin-right-large peg2 in stock$8
black tailfin-right-small peg4 in stock$8
THUNDERCRACKER
missile launcher4 in stock$3
long missile0 in stock$10
short missile0 in stock$7
large left wing with stickers-emblems -large peg0 in stock$6
large left wing worn/no stickers-large peg1 in stock$4
large left wing with stickers-emblems -small peg0 in stock$6
large left wing worn/no stickers-small peg1 in stock$4
large right wing with stickers-emblems -large peg1 in stock$6
large right wing worn/no stickers-large peg1 in stock$4
large right wing with stickers-emblems -small peg0 in stock$6
large right wing worn/no stickers-small peg1 in stock$4
black tail rudder-left-stickers-large peg0 in stock$5
black tail rudder-left-worn/no stickers-large peg4 in stock$4
black tail rudder-left-stickers-small peg0 in stock$5
black tail rudder-left-worn/no stickers-small peg0 in stock$4
black tail rudder-right-stickers-large peg0 in stock$5
black tail rudder-right-worn/no stickers-large peg2 in stock$4
black tail rudder-right-stickers-small peg0 in stock$5
black tail rudder-right-worn/no stickers-small peg0 in stock$4
blue tailfin-left-large peg0 in stock$8
blue tailfin-left-small peg0 in stock$8
blue tailfin-right-large peg0 in stock$8
blue tailfin-right-small peg0 in stock$8
DIRGE
large left wing with stickers-emblems 0 in stock$8
large left wing worn or no  stickers0 in stock$5
large right wing with stickers-emblems 0 in stock$8
large right wing worn or no stickers 1 in stock$5
bomb3 in stock$6
RAMJET
large left wing with stickers-emblems 0 in stock$8
large left wing with worn or no stickers0 in stock$5
large right wing with stickers-emblems 0 in stock$8
large right wing with worn or no stickers0 in stock$5
black left rudder with decal0 in stock$5
black left rudder with worn  or no decal0 in stock$4
black right rudder with decal0 in stock$5
black right rudder with worn or no  decal0 in stock$4
bomb1 in stock$5
THRUST
missile launcher2 in stock$5
long missile2 in stock$10
short missile2 in stock$7
large left wing with stickers-emblems 0 in stock$8
large left wing -worn or no stickers0 in stock$5
large right wing with stickers-emblems 0 in stock$8
large right wing- worn or no stickers3 in stock$5
black tailfin-left-with sticker0 in stock$5
black tailfin-left-worn or no sticker0 in stock$4
black tailfin-right-with sticker0 in stock$5
black tailfin-right-worn or no sticker2 in stock$4