Male Hose Tails have a Hose tail on one end and a Male BSP thread on the other end.
These are used to join flexible hose to a Female BSP fitting.
In the item listing the first size relates to the Hose size that will fit and the second size is the Male BSP thread..
Example: A 20 mm x 3/4" Male Hose Tail will suit a 20 mm hose on one end and on the other end the male thread will fit a 3/4" Female ( FI ) BSP Thread.
Regarding hose sizes the following is an approx conversion between metric and inch.
10 mm = 3/8" 15 mm = 1/2" 20 mm = 3/4" 25 mm = 1" 32 mm = 1-1/4" 40 mm = 1-1/2" 50- mm = 2"
'
If you have problems pushing the hose onto the tail, warming the hose with warm water will help, also to make this a leak free join you will need to use a clamp to clamp the hose to the hose tail. | 
