Quarks carry charges of two thirds and one third of e, yet no free particle has ever been caught with a fractional charge. Pick the flavours and the lab adds them up — in whole thirds, never in decimals — so you can see the total land on an integer every single time.
What are you building?
Slot 1quark
uUp · +2/3
Slot 2quark
uUp · +2/3
Slot 3quark
dDown · −1/3
Electric charge Q
+1 e
Thirds: +2 +2 −1 = +3, and +3/3 = +1.
Baryon number B
1
Three quarks and no antiquarks: (3 − 0) / 3.
Sum of quark masses
9.02 MeV/c²
u 2.16 + u 2.16 + d 4.70
Matched particle
Proton
The lightest baryon, and the reason ordinary matter is stable.
Quark mass as a share of the real particle
0.96%
The proton weighs 938.272 MeV/c². Almost all of that is the energy of the gluon field, not the quarks.
Fixed: quark masses are the PDG 2025 values —
u 2.16, d 4.70, s 93.5, c 1273, b 4183, t 172560 MeV/c².
Charges are exact thirds of e.
Try this: leave it on Baryon and step slot 3 from d back to u. The charge jumps from +1 to +2 — proton to Delta++ — and never once passes through a fraction on the way.