It depends. From a functional or a legal view?
It has been common and accepted practice to intermix Aeroquip 303 and Stratoflex 111 hose and fittings. The reason is that both are made to the same military specification (MIL-DTL-8794 for the hose) and are considered identical. I believe both Stratoflex and Aeroquip "discourage" the practice as neither one has control over the performance of the final product.
Aeroquip 601/701 and Stratoflex 156 (lightweight outside steel braid hose) the same argument could be said however the practice is not as common (ingrained) into the industry.
Teflon hose products: Not done.
Note that I fall back on "common and accepted practice" as the only justification. I cannot point to any authoritative document but just past practice in the industry. This is a thin leg to hand on as all it takes is one FAA inspector to wave his magic wand and disallow the practice. Often "accepted" practices become "unacceptable" as soon as a problem arises. Personally, I have no issues with intermixing hose and fittings on 303 or 111 style hose. I am more cautious with the other hose types.
Is it best to mate them to their own product line up?
Yes it is best to mate them to their own product line as that is how they are performance tested. For example, I know that when I build a Stratoflex 124-4 hose that its ultimate minimum burst strength is 12,000 psi. I know this by testing the product at random intervals not to exceed 500 hoses. If I deviate and build the product using some other method or use other fittings I do not know if it meets specification because there is no testing data that has been done.
There is another reason - As a mechanic one wants to shift as much potential liability "blame" as one can. Mixing manufacturer's gives each manufacturer an escape clause to deny responsibility if anything goes wrong. Do it per the manufacturer instructions and then if anything goes wrong it must be their fault.
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