How too short? Are you putting a 1/2" to 15mm compression fitting inside? As long as the 3/4" threads bottom out (into port on iBox) with a nice tight fit (plenty PTFE) then anything else will just tighten into the 1/2" threads. However I would probably just use one of these; http://www.6thplanet.com/store/product/plubr1bspmto22mm_l.jpg
(3/4" BSP to 15mm compression) Ditch the bushings/reducers and use this straight into the iBox then pipe off that...
Where abouts are you? I might know a good local plumbers' merchants.
How too short? Are you putting a 1/2" to 15mm compression fitting inside? As long as the 3/4" threads bottom out (into port on iBox) with a nice tight fit (plenty PTFE) then anything else will just tighten into the 1/2" threads. However I would probably just use one of these;
http://www.6thplanet.com/store/product/plubr1bspmto22mm_l.jpg
(3/4" BSP to 15mm compression) Ditch the bushings/reducers and use this straight into the iBox then pipe off that...
Where abouts are you? I might know a good local plumbers' merchants.
(trust me I'm a builder.....)