Alcon 0.625" Tandem Master Cylinder: M10x1.25 vs M10x1.5 Thread Ends

Both cylinders are identical where it counts for performance: same 0.625" forged body, same 230mm mounting centres, same 12mm stroke per circuit. The only difference is the outlet port thread pitch. Choose the M10x1.25 (MAR7200KM230C) if your build runs Japanese-platform OEM hard lines or standard motorsport braided-line fittings from Goodridge or Earls; M10x1.25 is the dominant pitch stocked by those suppliers and the most common metric pitch for race brake hard lines. Choose the M10x1.5 (MAR7200KM230B) only if the existing hard lines or caliper banjo bolts on your car are confirmed M10x1.5, a pitch associated with some European caliper applications. Getting this wrong before the car leaves the shop means lines that will not seal.

Spec Comparison

Specs sourced from the Alcon MAR72 product page.

M10x1.25 (MAR7200KM230C): The Default Choice for Most Builds

If you are starting from a clean-sheet brake line build or running a Japanese-platform car, M10x1.25 is almost certainly what you need. It is the pitch catalogued by Goodridge for single and double banjo bolts, bulkhead fittings, and direct-connect fittings in race applications. Earls lists both a banjo bolt and a -3AN to M10x1.25 inverted flare adapter as standard stock items. RaceFlux offers -3AN and -4AN male flare to M10x1.25 adapters rated to 1,000 psi. In short, the full ecosystem of braided line and AN conversion fittings is available off-the-shelf without special ordering.

The honest trade-off: there is no performance difference between the two cylinders. If your existing hard lines or caliper ports are M10x1.5, this unit will not thread in. Confirm your thread pitch before ordering.

M10x1.5 (MAR7200KM230B): When Your Lines Are Already Cut

M10x1.5 is the standard coarse pitch for a 10mm fastener, the default "M10" at any hardware counter, but it is not the standard for most OEM brake hard-line fittings and it is not the dominant pitch in branded motorsport line kits. Where it does appear is on some European caliper banjo bolt applications. If the car you are building has existing hard lines or caliper ports confirmed as M10x1.5, this is the correct cylinder; using the M10x1.25 version would result in a port that will not seal.

AN adapters are available from Fragola (650308 and 650404 for -3AN and -4AN respectively), Russell (640680 banjo bolt), TBM Brakes, and generic stainless suppliers, so the fitting ecosystem exists but requires a deliberate sourcing step rather than grabbing standard Goodridge or Earls catalogue items. Both cylinders seal identically via a copper washer face seal at the same 17 to 20 Nm torque spec, so there is no sealing method advantage to either pitch.

How to Choose

The decision reduces to one question: what thread pitch are the brake line ends or caliper banjo bolts already on your car?

To confirm, use a thread pitch gauge on the existing hard line nut or caliper port before ordering. M10x1.25 has a noticeably finer thread than M10x1.5; the difference is visible side-by-side but easy to confuse by eye alone. If you are routing all-new lines, M10x1.25 gives you the widest choice of off-the-shelf fittings from motorsport suppliers. If the lines are already cut and fitted to M10x1.5 ports, do not adapt; order the M10x1.5 cylinder and use the correct mating fittings throughout.

Both cylinders share the same seal kit (MAR7200-SK), the same forged body, and the same 230mm centre spacing, so if you ever need to swap thread specs after a platform change, only the master cylinder needs to change, not the mounting hardware.

For help choosing between bore sizes on the same platform, see our guide: Alcon Tandem Master Cylinder: 0.625" vs 0.700" Bore.