Short answer: Three connection types dominate two-component (AB) cartridges: bayonet (twist-lock), bell-mouth (retaining nut), and threaded (screw-in). Bayonet is fastest for frequent changeovers (Mixpac A-System, Nordson 50 mL); bell-mouth gives the strongest seal for larger volumes (Mixpac C-System, Cox); threaded is rare but used where vibration resistance matters. Your cartridge’s letter system — A, B, C or F — tells you which one you have. Here is the map, plus a 30-second way to identify yours.
The Three AB Cartridge Connection Types
1. Bayonet (twist-lock)
A male collar with lugs drops into a J-slot and twists to lock — the same “push and turn” motion as a camera lens. Pros: fastest changeover, tactile click confirmation, lowest cost. Cons: weaker axial seal than a thread, so less suited to very high-pressure or high-vibration runs. Used by Mixpac A-System and most 50 mL side-by-side cartridges.
2. Bell-mouth (retaining nut)
A flared collar is clamped by a threaded retaining nut (or cradle) on the gun. Pros: strong, repeatable seal for larger volumes and higher back-pressure; robust against pull-out. Cons: slower to fit than bayonet. Used by Mixpac C-System and standard 200/400 mL cartridges (e.g., Cox).
3. Threaded (screw-in)
The nozzle screws directly into the cartridge mouth. Pros: highest mechanical resistance to vibration and axial load. Cons: slowest; prone to cross-threading. Seen on some industrial tips such as Sherwin-Williams FASTLINE 2K cartridges.
A / B / C / F System Map
| System | Connection | Volume | Typical mixers | Made by |
|---|---|---|---|---|
| A-System | Bayonet | 50 / 75 mL | MAH, MAHX, MAQ | Mixpac; also Nordson EFD, generic |
| B-System | Interlock | 25 / 50 / 75 mL | MBH, MBHX | Mixpac (OEM-matched) |
| C-System | Bell-mouth | up to 400 mL | MCH, MCQ | Mixpac; generic bell |
| F-System | Interlock | 200 / 400 mL | MFH, MFQX | Mixpac (OEM-matched) |
Brand-by-Brand
- Mixpac (Sulzer): A = bayonet, B = interlock, C = bell-mouth, F = interlock. The clearest “letter = interface” scheme in the industry.
- Nordson EFD: side-by-side 50 mL+ cartridges use bayonet / bell — cross-fit with A-System nozzles.
- 3M Scotch-Weld EPX: its own EPX bayonet / bell on 48.5–50 mL and 200/400 mL; treat as a sub-family.
- Cox / standard cartridges: 200/400 mL bell / cradle; pair with bell-mouth mixers.
Identify Your Connection in 30 Seconds
- Look for the letter. A/B/C/F is printed on the barrel for Mixpac-format cartridges.
- Feel the mouth. Twist-lock lugs = bayonet (A). Flared collar + nut = bell-mouth (C). Keys/slots that resist a plain twist = interlock (B/F).
- Still unsure? A photo of the cartridge mouth and your gun tip is enough for a supplier to identify it — send it to us.
The Costly Mistake: Ordering the Wrong Interface
The most expensive error in 2K dispensing isn’t price — it’s the returned order. A bayonet nozzle can’t seat on a bell-mouth or interlock cartridge, and an interlock cartridge won’t accept a plain bayonet. Buyers who guess from a thumbnail end up with a pallet that doesn’t fit the gun. The fix is to identify the interface before you order, using the steps above or our compatibility guide for Mixpac series.
Choosing the Right System for Your Process
- Frequent small shots, manual gun: A-System bayonet (50 mL) — fastest swap, lowest cost.
- Larger volume, higher back-pressure: C-System bell-mouth (up to 400 mL) — stronger seal.
- Proprietary material / anti-cross-contamination: B or F interlock — OEM-matched only.
- High-vibration industrial line: threaded tip where available.
Frequently Asked Questions
What is the difference between bayonet and bell-mouth cartridge connections?
Bayonet is a twist-lock collar for fast changeovers on small cartridges (A-System); bell-mouth clamps a flared collar with a nut for a stronger seal on larger volumes (C-System).
Is a Mixpac A-System cartridge the same as Nordson EFD?
For 50 mL side-by-side formats, yes — both use bayonet / bell geometry, so A-System nozzles cross-fit Nordson EFD cartridges. Always confirm the ratio code.
Can I use a bell-mouth nozzle on a bayonet cartridge?
No. The interfaces are physically different; the nozzle won’t seat or seal. Match connection type to system letter.
Why are B and F systems “interlock”?
Interlock connections use keys that prevent A and B from crossing before mixing and resist cross-brand fit. They are patented and OEM-matched.
How do I avoid ordering the wrong cartridge?
Identify the system letter and interface before ordering, or send a photo of your gun tip to your supplier. See our cartridge range.
Conclusion
AB cartridge connections come down to three types — bayonet, bell-mouth, threaded — and your A/B/C/F letter tells you which. Bayonet for speed, bell-mouth for seal, interlock for proprietary formats. Match the interface before you buy, and when the label is gone, a photo settles it. Explore Haijing cartridges by system or pair them with the right mixer.
