How to size HDPE fittings

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Andy Ritger

New Member
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San Jose, CA
I'm running several hundred feet of IPS DR11 2" HDPE from my water holding tanks to various risers in my orchard. The supplier had the HDPE in stock, but not the fittings. So, I ordered the fittings separately. But, now I'm concerned that I didn't get the right size fittings.

The DR11 2" HDPE has an average interior dimension of 1.917", according to what I think is the catalog for it: HDPE-Pressure-Piping-Complete Catalog-en.pdf

However the fittings I have are:

Dixon RDM26 insert x insert pipe mender; exterior dimension exactly 2", according to

Dixon RST25 insert x male king nipple; exterior dimension 2 1/32", according to

I haven't worked with HDPE before. When I heat it with a propane torch, how much can I expect it to stretch/expand? If these fittings are too large, what is the right way to shop for the correct sized fittings?


In the Trades
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Berkeley, CA
I don't have hands-on experience, but my understanding is that PE pipe like this comes in two types: controlled outer diameter (DR or SDR, same meaning) and controlled inner diameter (SIDR). For SIDR pipe, you use insert barb style fittings that reference the inside diameter. For DR pipe, you use compression style fittings that reference the outside diameter. [And in 2", DR ~15 has inner diameter matching the SIDR pipes (which are based on Schedule 40 inner diameters), so you could use either.]

Cheers, Wayne
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