KYB Gas-a-Just vs Excel-G
KYB sells more than one shock and strut line, and the part number decides which one you get. Excel-G and Gas-a-Just are the two lines this store lists most often. They are not different names for the same part. A vehicle page shows the line on each part, and a vehicle may list only one of them.
Excel-G
Excel-G is a twin-tube, gas-charged shock or strut. It is built to restore the ride and control the vehicle had when it was new, rather than to make the suspension stiffer than stock. Choose it for ordinary driving when the catalog lists an Excel-G part in the position you need. KYB 349108 is an Excel-G rear shock, and KYB 341259 is an Excel-G rear strut for the 1997–2000 Mazda Millenia.
Gas-a-Just
Gas-a-Just is a high-pressure monotube. The gas and the oil sit in separate chambers, so the piston works in fluid instead of a mix of fluid and bubbles. Compared with Excel-G, it is the firmer, faster-responding line. Look at it when the vehicle tows, carries a load, or runs larger wheels, and when the catalog actually lists a Gas-a-Just part. KYB KG9135 is a Gas-a-Just front shock. A 2015 Ford F-150 listing shows both lines, including Gas-a-Just and Excel-G rear shocks.
What the catalog will not invent
Not every vehicle has both lines. If the vehicle page lists Excel-G only, this catalog has no Gas-a-Just part for that position. The series name on the part is the source of truth. Strut-Plus is a different product: a strut, coil spring, and mount already assembled. It is not a third damping tune of Excel-G.
How to pick
Look up the year, make, and model. Match the position, including left or right when the part is sold that way. When the quantity says two per vehicle, replace both sides of that axle so a new damper is not paired with a worn one. The part page links to the vehicle pages that exist for that part and to the companion part for the other side or the other end of the vehicle when those parts are in the catalog.