Strap Boss & Boss Connectors
A boss is how a small waste pipe joins a large soil stack. The strap boss clamps onto the outside of the stack over a cut hole, giving a sealed 36, 43 or 55mm entry without needing a purpose-made branch fitting at that exact position.
Also searched as: strap boss, boss connector, boss adaptor, saddle boss, waste connection to stack
Strap boss versus boss pipe
A strap boss is retro-fitted: a hole is cut in the stack and the boss is strapped and sealed over it, which lets the waste connection be positioned exactly where the appliance needs it. A boss pipe has one or more bosses moulded in at fixed centres and is used when the layout is known at design stage.
Sizes and appliances
Bosses accept 36mm (basin), 43mm (sink, bath, shower) and 55mm (multiple appliances or long runs) waste pipe. The 160mm strap boss is used where a waste joins a main collection run rather than a floor stack.
Where not to use one
Do not fit a boss within the restricted branch connection zone opposite the WC entry, and do not cut a boss hole through a fitting or across a joint. The hole must be in the barrel of the pipe, cleanly cut and de-burred, or the seal will weep.