Metal Bit Chip
Probably the rarest part in the entire generation (even including recolours - currently only nine are known, and prior to June 2021, only four were known). It was given out at BBA tournaments in some capacity in the early days of Beyblade (pre A-Series release). It was accompanied by a CoroCoro Dragon sticker with name katakana larger than standard, and positioned over both the centre section and border of the sticker.
Highly potent - it is a sizeable weight advantage that makes combinations much harder to KO and improves grinding ability and recoil control significantly
As such, it is a top tier choice on almost all types except Zombies, with particular notability on Circle Survivor Defense, Force Smash, and Defensive Zombies, which don't mind the alteration to stability (though Defensive Zombies do require more specific Part choice), as well as Attack where feasible. It is also a great option to improve Defense on basically any Beyblade, or to reduce Recoil.
There is however a natural tradeoff from having a heavy weight at the centre and top of the Beyblade - it increases top heaviness, causing the Beyblade to tilt faster. As such, for certain match ups (for example, Defensive Zombies vs Circle Survivor Defense), one should consider using other parts that result in more stability to compensate (such as using SG (Bearing Version 2) Casings over Double Bearing Core with SG (Bearing Version 2) Shaft).
In addition, this reduction to stability can mean losing mirror matches, as most opponents will be running similar combos but without the MBC.
It is also constrained by the requirement for the Short Bit Chip retention tabs to still be intact - this limits use with Attack and Defense combinations that do not have some form of protection for them.
On the whole, the Metal Bit Chip is a strong part, but the context of ones local meta should be considered should you be fortunate enough to own one. Often, the Bit Chip Figure/Power Spirits Bit Chip is more practical despite being approximately 1g lighter.