Box Box Rear Derailleur
What the checker says70will not fit
Run variant by variant through the mountain bike builder’s own engine. Every sentence below is the checker’s, unedited. Nothing here says this part fits your bike; it says what it does and does not fit among the parts we hold.
Checked against 6099 verified mountain bike parts in this catalog. 5908 produced no finding of any kind. Each variant produces 58 distinct errors and 0 distinct warnings.
Will not fit
- Will not fiterror · CassetteSpeed mismatch: Derailleur 9s, Cassette 12s. Shifter, derailleur and cassette must be the same speed count. On 31 of the 60 verified cassettes in this catalog. Applies to all 3 variants.
- Will not fiterror · ShifterSpeed mismatch: Shifter 12s, Derailleur 9s. Shifter, derailleur and cassette must be the same speed count. On 28 of the 53 verified shifters in this catalog. Applies to all 3 variants.
- Will not fiterror · ShifterDrivetrain mismatch: Shifter = Shimano 12-speed, Derailleur = Box Prime 9 (9-speed). Shifter, derailleur, cassette, chain and front derailleur must be one system. On 19 of the 53 verified shifters in this catalog. Applies to all 3 variants.
- Will not fiterror · CassetteDrivetrain mismatch: Derailleur = Box Prime 9 (9-speed), Cassette = Shimano LinkGlide (CUES). Shifter, derailleur, cassette, chain and front derailleur must be one system. On 16 of the 60 verified cassettes in this catalog. Applies to all 3 variants.
- Will not fiterror · CassetteDrivetrain mismatch: Derailleur = Box Prime 9 (9-speed), Cassette = Shimano 12-speed. Shifter, derailleur, cassette, chain and front derailleur must be one system. On 15 of the 60 verified cassettes in this catalog. Applies to all 3 variants.
- Will not fiterror · CassetteCassette too big: 52T cassette exceeds the Box Box One Prime 9 X-Wide max of 50T. On 13 of the 60 verified cassettes in this catalog. Applies to 1 of 3 variants.
- Will not fiterror · CassetteCassette too big: 52T cassette exceeds the Box Box Three Prime 9 X-Wide max of 50T. On 13 of the 60 verified cassettes in this catalog. Applies to 1 of 3 variants.
- Will not fiterror · CassetteCassette too big: 52T cassette exceeds the Box Box Two Prime 9 X-Wide max of 50T. On 13 of the 60 verified cassettes in this catalog. Applies to 1 of 3 variants.
Drivetrain system, Chain. 15 more findings from the same check, on up to 9 of the 45 verified chains each.
Drivetrain system, Shifter. 11 more findings from the same check, on up to 11 of the 53 verified shifters each.
Actuation, Shifter. 9 more findings from the same check, on up to 1 of the 53 verified shifters each.
Drivetrain system, Cassette. 9 more findings from the same check, on up to 9 of the 60 verified cassettes each.
Drivetrain speeds, Cassette. 4 more findings from the same check, on up to 11 of the 60 verified cassettes each.
Drivetrain speeds, Shifter. 4 more findings from the same check, on up to 10 of the 53 verified shifters each.
Drivetrain system, Front Derailleur. 4 more findings from the same check, on up to 12 of the 34 verified front derailleurs each.
Cassette capacity, Cassette. 3 more findings from the same check, on up to 10 of the 60 verified cassettes each.
Gearbox derailleur, Gearbox. 3 more findings from the same check, on up to 6 of the 6 verified gearboxs each.
Open a variant in the builder to see the ones that apply to your own parts.
$83.99 to $165.74 MSRP·290 g
What the maker states
- System
- Drivetrain system Box Prime 9 (9-speed)
- Speeds
- 9-speed (rear index count the maker rates it for)
- Actuation
- Mechanical (cable)
- Maximum cog
- Largest cog 50 teeth
- Mount
- Standard hanger
3 verified variants
| Variant | Price (MSRP) | Weight | Source | Last checked | Build |
|---|---|---|---|---|---|
| Box Three Prime 9 X-Wide (2019) | $83.99 | 290 g | maker’s page | 2026-07-14 | Build with this |
| Box One Prime 9 X-Wide (2019) | $165.74 | 290 g | maker’s page | 2026-07-14 | Build with this |
| Box Two Prime 9 X-Wide | $120.69 | not stated | maker’s page | 2026-07-31 | Build with this |
The rest of what the maker states2 not published
2 further fields the checker looks for are not published by Box, so we leave them blank rather than estimate them, and those 2 checks stay silent on this rear derailleur. They are maximum cog top and total capacity. Each is recorded as “not stated by the maker (not checked)”.
Source: each variant links the maker’s own page in the table above. Last checked 2026-07-14 to 2026-07-31.
Checked against
The checker ran this model against every verified part below that it has a slot for, the same way it checks a build in the builder. What follows is the verdict it actually produced for that specific pairing — not a recommendation, and not a guarantee any of these parts fits your own bike.
- 5DEV R-SPEC Trail/Enduro Cranks (Crankset) No conflicts found
- 9point8 Fall Line (Dropper Post) No conflicts found
- 9point8 Stout (31.8, 30mm) (Stem) No conflicts found
- ACID SLX 30 front (Front Wheel) No conflicts found
- ACID SLX 30 rear (Rear Wheel) No conflicts found
- Acros ZS44/ZS56 (Headset) No conflicts found
6 of 1858 counterparts with a page of their own that the checker actually probed this model against, in alphabetical order by brand and model — never by price, popularity or the verdict itself.