"T" refers to the Thumb-turn side (or the inside of the lock). For example, 45T55 refers to 100mm Cylinder with the thumbturn being in 45mm side of the cylinder. The Thumb Turn needs to be in the inside of the door.
eBay
Thumb Turn Euro Cylinder Lock – UPVC Front Door Barrel Anti Snap Mila BreakSafe.
eBay
Overall size of cylinder is 95mm : 50T/45 - T signifies THUMBTURN, which should be the internal side. Cylinder is keyed on external side and thumbturn on the other and features Anti-Bump, Anti-Pick, and Anti-Drill protection.
eBay
Anti-Snap: The cylinder has sacrificial cuts that will snap if the cylinder is subject to attack. We can provide a variety of sizes with a thumb turn. The "T" represents the thumb turn, so if you require a thumb turn on the 35mm side of a 35/45 cylinder, you would need to select a "T35/45".
eBay
1x cylinder thumb turn lock 50 internal - 45 external.
eBay
Accredited with TS007 British Standard 1 Star and Sold Secure Gold, it boasts an impressive array of anti-attack features, such as anti-snap, anti-bump, anti-pick and anti-drill. TS007 1 Star British Standard Kitemark.
eBay
Thumb Turn Euro Cylinder uPVC Door Lock Barrel 3 Star T007 5 Keys GreenteQ Orion.
eBay
Flat reversible dimple key with Yale logo and stylish nylon key bow. 1 x Yale Key card. - Flat reversible dimple key with new stylish nylon key bow. The Platinum 3 Star cylinder is independently tested by BSI to be awarded the British Kitemarked TS007:2014 3 star accreditation.
eBay