Metric (Euro) to Standard PVC Couplings and Unions.  In the reefing hobby, there are a ton of products that come from all over the world that uses metric sizing.  These allow you to easily convert European Metric-sized plumbing to Standard US PVC.

Size Chart

20mm to 1/2"

25mm to 3/4"

32mm to 1"

40mm to 1-1/4"

50mm to 1-1/2"

In-Line Probe Holder and 

Dual 1/2" Manifold

Instructions