Brass Compression Fitting For Plastic, Copper, & Aluminum Tubing, 0.31 Inch Tube OD To 1/4-18 Male NPT, Straight

With plastic tubing, the 250F upper limit may not apply the same way it does with metal. That rating is confirmed for metal tubing like copper or aluminum. Plastic tubing has its own temperature ceiling depending on the material, so you'd want to cross-check whatever tubing you're running against its own rated range before assuming the fitting's full temperature window carries over.