Blade, Ratchet and Bit: what each Beyblade X part actually does
Three parts, and the combination is the point
Takara Tomy's own description of the basic structure is that a Beyblade is made of three parts and that changing the combination changes its performance. That is the whole design: the parts are interchangeable across releases within Beyblade X, so two blades and two bits are four set-ups rather than two.
Blade — the part that does the hitting
The Blade is described as the main part, the one that collides with the opponent directly, and its performance differs with its shape and its weight. It is the part a release is named after, so "Wizard Arrow" or "Shark Edge" is a blade name, not a whole-top name.
Ratchet — the part that sets the height
The Ratchet is the middle part, and Takara Tomy describes it as the one that decides the Beyblade's height — which in turn sets the centre-of-gravity balance and how the blade makes contact. This is what the two numbers in a code such as 4-80B are doing: they describe the ratchet.
It is also the part most worth buying separately. A blade you already own behaves differently on a taller or shorter ratchet, which is a cheaper change than a new blade.
Bit — the part that decides how it moves
The Bit is the tip, and it is described as the part that decides the Beyblade's movement, with dash performance and burst resistance changing with it. The letters at the end of a code — the B in 4-80B, the LF in 3-60LF — are the bit.
It is also the part that decides the top's type: Takara Tomy states that a Beyblade's type is determined by its bit, and that there are four types with advantages against each other. So swapping a bit is not a tuning change, it is a change of role.
The bit is what the Xtreme Dash runs on, too — the super-acceleration Takara Tomy tells new players to work towards once the basics of shooting are in place.
BX, UX and CX are three different part philosophies
BASIC LINE (BX) uses a metal launcher hook, which Takara Tomy attributes to keeping the weight balance stable. It is the line to buy parts from first, because it is the largest and the least specialised.
UNIQUE LINE (UX) swaps that hook for a resin one specifically so that more of the blade's metal can be distributed to the outer edge, and Takara Tomy describes the line as specialised towards distinctive performance. Same three-part structure, different trade-off.
CUSTOM LINE (CX) goes further: the blade itself comes apart into a Lock Chip, a Main Blade and an Assist Blade, which is what makes the line customisable. If you buy CX you are buying more parts per box, and more to swap.