the brake cylinders should have the bore size cast into the casing on the area where the bleed nipple and brake line screw in
I've had both mine replaced this week with NOS unipart ones and they had the bore size on them.
I have trackerjack brakes and have gone with std sprint (the larger bore) cylinders
Hope this helps
_________________
1976 Taihiti Sprint
2020 Jaguar iPace ev400
2011 Landrover Defender pickup - twisted
2023 Porsche 911 Carrera T Manual!!
2021 Toyota Yaris GR-Four
2011 Super Skoda Fabia 1.2 S HTP
Gone but not forgotten 2008 BMW M5 (E61) Touring (George, as in Best, as it likes a Drink) to be replaced soon...... Epic epic car