This spacer makes a 1" (inner diameter) suction hose fit snugly into a 50mm (inner diameter) pipe, commonly used for plumbing (for instance this one) - or as it may, to provide a ventilation hole for a garden well. The intent isn't to provide an airtight gap, rather a means of preventing small animals or insects of suiciding down said well.

It was designed and tested with a specific Gardena hose in mind (model 1411-20 or 1418-20) , but could reasonably work with other brands if the dimensions are similar.