The 
Fluidmaster PRO45B is a high-performance, professional-grade bottom-entry toilet fill valve designed as a superior replacement for traditional ballcocks in cisterns. Its key feature is a heavy-duty brass shank for enhanced durability and reliability. 
Key Features and Specifications
Heavy-Duty Brass Shank: Unlike cheaper plastic alternatives, the brass shank resists cracking, corrosion, and cross-threading during installation, which is a major reason professional plumbers prefer it.
Ultra-Quiet Operation: The design significantly reduces noise during refilling and is engineered to minimize or eliminate water hammer (the banging pipe noise), providing smooth and quiet performance.
Universal Fit: The valve is height-adjustable from 230mm to 355mm (approximately 9 to 14 inches), allowing it to fit most brands and sizes of toilet cisterns, including modern 6-litre models.
Anti-Siphon Design: It features an anti-siphon mechanism to prevent the contamination of the fresh water supply, meeting code approvals.
High and Low Pressure Compatibility: The valve works efficiently across a wide range of water pressures (from 0.2 bar up to 15.85 bar).
Easy Installation and Maintenance: Designed for straightforward installation, the valve also allows easy access to seals for simple maintenance.
Warranty: The PRO45B comes with a 5-year warranty, highlighting its durable construction.
Connection Size: It features a standard 1/2-inch BSP (British Standard Pipe) bottom inlet connection.