Why won’t the hose fit onto the combination nipple?

Fortunately, this is not a problem with either the hose or the COMBINATION NIPPLE,” a product which is also commonly referred to as a “KING NIPPLE” or a “HOSE ADAPTER”. Generally, it turns out that this problem is a case of having purchased the wrong product.

The insert barb outer diameter (O.D.) dimension for hose fittings is smaller than the O.D. of poly pipe insert fittings. Designed for polyethylene (PE) plastic pipe manufactured to the ASTM-D2239 standard, the chart below shows the difference in the barb O.D. for a fitting of the same nominal size.

Typically, customers have issues with either ½” or 1-1/4” fittings for which the percentage difference is the greatest and it is impossible to get the hose to go onto the fitting. In some cases, depending on the hose reinforcement, hoses can be installed on the other sizes, however the fit is extremely tight.

When ordering fittings to be used with a hose, we offer the following:

How can one identify a hose insert fitting from a poly pipe insert fitting?

For most people it is very difficult to easily distinguish between the two diameters of fittings visually.

Boshart makes the identification easy by machining two distinctly different barb profiles so that the installer can visually distinguish between the different designs.

TIP! - Poly Pipe is only made in pipe sizes ½” and larger, therefore a fitting smaller than a nominal size of ½” will be designed for hose.

For brass hose fittings for hoses 1/8” up to 1-1/4” see the BH-Series Fittings in section 3 of the catalog:

https://boshart.com/wp-content/uploads/product-assets/ee7e2fc0dd4d92c6b38f01cbce9da473e18bdf94_Boshart_Product_Catalog_Section3.pdf

Additional Resources:

https://support.boshart.com/how-to-install-a-worm-gear-hose-clamp

https://support.boshart.com/can-the-107-series-nylon-reinforced-flexible-pvc-hose-be-used-in-vacuum-application

https://support.boshart.com/why-do-insert-fittings-for-poly-pipe-pe-have-barbs-with-slightly-larger-diameters-than-the-i.d.-of-the-pipe

https://support.boshart.com/what-is-the-difference-between-2-sscxxxx-and-sscxxxx-worm-gear-hose-clamps