The list of fittings is listed below. Note that I used elbows to make the routing easier since the teflon tubing does not easily bend without kinking. I bought 18" or so of teflon tubing.Here's a description of how things are routed:The teflon tubing comes out of the 90 degree pump fitting, goes across the machine and down to the OPV which sits on the bottom right of the machine. The teflon tubing to OPV connections are using 1/8 BPP fittings and compression bicones and nuts from orphan espresso. I wrapped the OPV with rubber weather stripping so that vibrations don't pass to the machine case. Out of the OPV, the teflon comes back up and across the machine to near the pump output. (that way I can run it with or without the preheat fairly easily.) There is one cole-parmer compression fitting, a 90 degree elbow, and another cole-parmer compression fitting to transition to the 1/4 OD flexible copper preheat. The preheat coil wraps from the bottom of the boiler to the top, counter clockwise, ending at the top back right of the boiler. At the end of the final preheat coil, another cole-parmer compression fitting, 90 degree elbow, and another cole-parmer compression fitting to transition back from 1/4 OD copper to teflon. There's a very short (around an inch) teflon tube down to the gaggia inlet fitting. since I started with a Gaggia Coffee, not a Gaggia Classic, mine came with the inlet that did NOT have a built in OPV.out of the pump to teflon tubing (6mm OD x 4mm ID):http://www.espressoparts.com/V_549teflon tubing to 1/8 BPP:http://www.orphanespresso.com/Bicone-NUT-Brass-Fitting-14-for-6mm-Tubing_p_4865.html4859 Bicone 6mm Brass Fitting from orphan espresso 1/8 BPP fittings to OPV:assorted elbows and tees from Orphan Espressohttp://www.orphanespresso.com/search.asp?keyword=1%2F8&search=FindOPV:https://www.chriscoffee.com/SearchResults.asp?Search=ev321&Submit=Search1/8 BPP fittings to 6mm teflon:same bicone & nut as above6mm OD teflon tubing to 1/4 NPT:http://www.coleparmer.com/Product/Compression_To_Thread_Adapter_Stainless_Steel_6mm_OD_Tubing_X_1_4_NPT_M/EW-31528-021/4 NPT 90 elbow1/4 NPT to 1/4 OD flexible copper (preheat coil):http://www.coleparmer.com/Product/Compression_Fitting_Male_Pipe_Adapter_Straight_316_SS_1_4_OD_x_1_4_NPT/EW-31406-35preheat coil out end:http://www.coleparmer.com/Product/Compression_Fitting_Male_Pipe_Adapter_Straight_316_SS_1_4_OD_x_1_4_NPT/EW-31406-351/4 NPT 90 elbow1/4 NPT to 6mm OD teflon tubing:http://www.coleparmer.com/Product/Compression_To_Thread_Adapter_Stainless_Steel_6mm_OD_Tubing_X_1_4_NPT_M/EW-31528-026mm OD teflon to boiler inlet:http://www.shop.partsguru.com/B-0111-Gaggia-water-inlet-fittingO-ringLube-B-0111.htm
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