John Guest Part number: CI320814S 1/4" Pushfit x 1/2" tap adapter BSP Thread.

There's also an option to choose a CI321214S 3/8' x 1/2'' tap adapter BSP thread. 

The most reliable and leak free connections you can buy. 

Securely connects 1/4" or 3/8'' tubing to the adapter.

• Push fit technology
• Quick disconnection without the need for tools
• Food quality and suitable for potable liquids
• Suitable for soft metal or plastic tubes
• Superior flow characteristics
• NSF and WRAS approved