shower query

[FRANKIEJUNIOR]

Im going to plumb in an electric shower for a neighbour. Its a creda 8500DL model,cheap from argos. My concern is the water inlet fitting that comes with the shower unit. It is a plain 15mm st shaft unthreaded. What is the best fitting to use on this and would the olive get a good enough bite on this plastic st shaft if i used a comp elbow without blowing off. The limited space inside the unit is too bulky for a hep elbow.
Any advice is much appreciated

 

[seco services]

as you have said a comp fitting will grip no problem.
i useally fit the comp fitting before fitting the shower then you can slacken it back off and the olive has gripped fit shower then just nip the comp up when pipework fitted.