ABS adapter for Schutz ibc

I have several IBC tanks from different brands that I successfully connected to a standard 2" ABS female adapter from the hardware store. I have one tank that for some reason doesn't connect. It's the right diameter, but the fine thread seems to be a tiny bit different and it just doesn't grab to the ABS adapter. Is there a different way to do this?

A photo or two would help me understand the situation better and come up with a suggestion.
Most of our PVC piping in the States is a standard thread commonly called "iron pipe" (MIP, FIP). If the thread on the tank doesn't match, it's probably a metric size/gauge and good luck finding a matching adaptor. You could try removing the threads from either the tank outlet or the inside of the ABS adaptor and creating a slip fitting. Then, just use a PVC or ABS glue to connect them. Glued connections in PVC/ABS are quite common and watertight, even under pressure.

Amazon sells 3 different sizes of IBC adaptor to garden hose.  They're about $8.

Sounds like you have a buttress S60x6. I spin weld fittings on some totes when using the as heat storage in the green house. https://www.totalwatersupplies.com.au/blogs/articles/how-to-determine-your-ibc-valve-thread

Joshua States wrote:A photo or two would help me understand the situation better and come up with a suggestion.
Most of our PVC piping in the States is a standard thread commonly called "iron pipe" (MIP, FIP). If the thread on the tank doesn't match, it's probably a metric size/gauge and good luck finding a matching adaptor. You could try removing the threads from either the tank outlet or the inside of the ABS adaptor and creating a slip fitting. Then, just use a PVC or ABS glue to connect them. Glued connections in PVC/ABS are quite common and watertight, even under pressure.

See below for some pictures. First two are from the tank where the standard ABS does not fit. Last two are from the tank where it fits perfectly. Thread seems the same to me. Besides these two, I have another two tanks where standard ABS fits right away.

Doesn't fit...

Fits perfectly...