In this photo I have lined up some of my wire crimper's. The one on the far left IS NOT A CRIMPER! I only say this because I have witnessed people putting together marine terminations with a pair of PLIERS!!
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The next crimper, the one with the yellow handles, is a cheap hardware store quality crimper and should only ever be used in an absolute emergency.
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The middle crimper is a decent quality Klein crimper though it's not really well suited for much other than crimping non-insulated terminals.
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The fourth crimper is a good quality crimper, made by Ancor Products, and designed specifically for crimping marine or aviation grade heat shrink terminations. The jaws of this crimper are precision machined, and wide enough in cross section, to produce an excellent crimp. This crimper is also of the ratcheting type and will not release until a proper crimp has been made.
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The final crimper shown is another ratcheting type crimper but this one, set up with the jaws shown, is designed for insulated terminals.
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Read on for more details on these different crimpers.
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NOTE: There is no such thing as a "marine grade" terminal. I refer to "marine grade" only because that is what the retailers tout them as and what most boaters know them as. "Marine Grade" is just a high quality insulated or heat shrink crimp termination. The same terminals are sold into aviation, industry and marine applications. In aviation they are often referred to as aviation grade... The difference with aviation terminals is that they need to meet minimum standards and be crimped with "certified" tools all of which are FAR MORE EXPENSIVE than the average boater is willing to buy. I personally use aviation certified tools but the ones below will get you you to "better than average"...