The inside diameter could be the measurement of the hole while in the pipe, though the outside diameter is the distance from just one side on the pipe to one other. In the United Kingdom the Experienced overall body would be the Chartered Institute of Plumbing and Heating Engineering (educational https://us.enrollbusiness.com/BusinessProfile/7405509/Alpine-Plumbing-Heating-And-Air-San-Dimas-CA-91773