Parts & materials

Guides

O-rings:
www.parker.com/literature/ORD%205700%20Parker_O-Ring_Handbook.pdf (Parker O-ring handbook)
www.cog.de/fileadmin/downloads/ORing_englisch.pdf (O-ring  basics)
http://www.hitechseals.com/includes/pdf/o-ring_brochure.pdf
https://static.eriksgroup.com/en/o-ring/Technical%20Handbook/Technical%20handbook%20O-rings%20update%20april%202013.pdf
https://content.gallagherseals.com/Definitive-O-Ring-Design-Guide (X-rings, Quad-rings part of previous link)

Plastics:
www.curbellplastics.com/technical-resources/pdf/plastic-material-selection.pdf
http://www.bpf.co.uk/Plastipedia/default.aspx (Plastipedia)

Plastics machining guides:
www.boedeker.com/fabtip.htm
www.curbellplastics.com/technical-resources/pdf/plastics-machining-guidelines.pdf

Links:

Metals, plastics, pipes, raw materials etc:
www.piping.georgfischer.com (Global) (PVC-U pipes, connectors and fittings)
www.vink.com (Europe) (source for raw plastics and for +GF+ parts)

Glue for plastics:
www.griffon.eu/en/products/838-rigid-pvc-solvent-cements/product/373-uni-100/
www.henkel.com/pipe-adhesives-cleaners-17553-17632.htm

Ready made rebreather bits and parts:
tecme.de (Germany)
www.watersafetyshop.com/ddparts.html (Germany)
www.golemgear.com/c-15-rebreather-products.aspx (USA)
www.northeastscubasupply.com (USA) (CEJN connectors, spares etc.)
www.divegearexpress.com (USA)
www..diveaddicts.com (USA)
www.opensafety.eu
http://hikerdiver.ch/shop/vbso/ (O2 MAV with integrated needle valve)

Gas connectors:
www.cejn.com (Global) (look for DN4, DN6, 221, 345 and 348 series)
www.swagelok.com (Global) (look for QC6 DESO series)
www.tomcoquickcouplers.com/ (Swagelok compatible couplers)
www.snap-titequickdisconnects.com (Global) (71 series 1/4" size used in Cis-Lunar)

Electrical connectors:
seaconworldwide.com/products/electrical-wet-mate/micro-wet-con
www.lemo.com/en/products/high-pressure-connector/w-connector

Needle valves, orifices, solenoids etc.:
www.camozzi.com (Global) (some use SCO 602-M5 and SCO 604-1/8, PDF)
www.okcc.com (Global) (orifices)
www.swagelok.com (Global) (S series needle valve, 0.032" orifice, PDF)
www.porterinstrument.com/ (Global) (VCD-1000 valve)
www.lenoxlaser.com/ (Global)(SS orifices in many forms)
www.clippard.com/ (solenoids, valves, fittings)
www.jaksa.si/index.html (solenoid valves)
www.norgren.com/ (Norgren KIP solenoid valves)
www.tom-parker.co.uk/ (pneumatic and hydraulic products, DIY P-valve parts)
www.birdprecision.com/orifices/ (Global, ruby and sapphire orifices in many forms)
http://www.parker.com/literature/Porter%20Instrument%20Division/Flowmeters,%20Metering%20Valves%20&%20Flow%20Controllers%20(FM-1058%20Rev.%200).pdf

Panel meters:
www.lascarelectronics.com (Global) (DPM 1AS-BL used in KISS display)

Fabrics:
www.seattlefabrics.com/ (USA) (heat sealable nylons, cordura etc.)
www.solastape.com/ (reflective tape)
www.extremtextil.de (Germany)(good selection of fabrics including heat sealable)

Bellows:
www.cqm-inc.com/index.asp (USA)
www.halltech.com/bellows.html (Germany)

Corrugated hoses:
www.redarling.com
www.crushproof.com

Cables & glands
www.pflitsch.de/en/cable-glands/blueglobe
www.agro.ch/ (they even got glands for multiple cables)

Sensors, oxygen:
www.sstsensing.com/product/miniature-mounted-oxygen-sensor (Zirconia based miniature sensor)

Sensors, pressure:
www.meas-spec.com/product/pressure/MS5837-30BA.aspx (miniature, I2C, available at Digikey & Mouser)
www.meas-spec.com/product/t_product.aspx?id=8685 (used in many rebreather controllers)

Thread inserts:
www.timesert.com/