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- Aug 16, 2008
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After receiving my ZT 0550 and enjoying the outstanding build quality of this knife, I also started to notice some refinements made to the 0550 after the launch of the 0551. I can't say I prefer the 0550 over the 0551, especially the blade steel because the 0551 has had some break in time and each of these knives perform incredibly well as far as operation goes. But key is that the 0550 is noticably smoother that then 0551, even right OOTB while the -551 needed some time to approach the smoothness of the 0550. Here are some of the refinements I've noticed so far:
** In each side by side where you can't tell which knife is which, the 0551 is alwasys on the left **
* The flat grind on the blade "appears" to go higher up the blade width toward the spine. It's hard to see sometimes because it also appears ZT repositioned the LASER etchings on each side so you may not be able to use the etching placement as a benchmark. I also measured the thickness where the edge bevel starts on the blade and both knives are .40 inches so the edge grind is not thinner. It all could just be an lluision from the repositioning of the LASER etched lettering too
* This also may be an illusion but I always thought the 0551 had a VERY minute recurve to the blade at the edge while it also "appears" that this is not the case with the 0550 - as if it has a micro amount more belly
* The LASER cut outs on the Ti slab are different between each knife. Look at all the cuts, starter holes and gaps
* All screw holes on the 0550 have a counter sunk bevel on the Ti, including the lanyard hole
* Edge bevels on the handle slabs are different. On the lockbar, the G10 and the Ti edges. You can see by the clip positioning and mount location
where this lends a slightly larger area with less weakening when screws are placed near this bevel
* There is no detent ball hole on the outside portion of the lockbar on the 0550
* The lockbar bend cut out on the 0550 seems a little further back than the 0551's
* The jimping grinds are different on the bottom of the handle
* The lanyard hole appears to be larger on the 0550
* The sharpening choil seems larger on the 0550
* The hex side of the pivot appears more flush to the Ti on the 0550
* The lockbar thumb cut out on the handle is more symetrical on the 0550 - more of a quarter moon shape than the 0551
* The contact area for the lockbar on the tang appears to have a more acute angle on the 0550 - this may decrease the sticky lockbar many of the 0551's had - time will tell I suppose. My 0550 has no lockbar stickiness at all while my 0551 did for a while. This may reduce any lock rock development too
* Anything else I may have missed?
Pictures beginning in the next three posts
** In each side by side where you can't tell which knife is which, the 0551 is alwasys on the left **
* The flat grind on the blade "appears" to go higher up the blade width toward the spine. It's hard to see sometimes because it also appears ZT repositioned the LASER etchings on each side so you may not be able to use the etching placement as a benchmark. I also measured the thickness where the edge bevel starts on the blade and both knives are .40 inches so the edge grind is not thinner. It all could just be an lluision from the repositioning of the LASER etched lettering too
* This also may be an illusion but I always thought the 0551 had a VERY minute recurve to the blade at the edge while it also "appears" that this is not the case with the 0550 - as if it has a micro amount more belly
* The LASER cut outs on the Ti slab are different between each knife. Look at all the cuts, starter holes and gaps
* All screw holes on the 0550 have a counter sunk bevel on the Ti, including the lanyard hole
* Edge bevels on the handle slabs are different. On the lockbar, the G10 and the Ti edges. You can see by the clip positioning and mount location
where this lends a slightly larger area with less weakening when screws are placed near this bevel
* There is no detent ball hole on the outside portion of the lockbar on the 0550
* The lockbar bend cut out on the 0550 seems a little further back than the 0551's
* The jimping grinds are different on the bottom of the handle
* The lanyard hole appears to be larger on the 0550
* The sharpening choil seems larger on the 0550
* The hex side of the pivot appears more flush to the Ti on the 0550
* The lockbar thumb cut out on the handle is more symetrical on the 0550 - more of a quarter moon shape than the 0551
* The contact area for the lockbar on the tang appears to have a more acute angle on the 0550 - this may decrease the sticky lockbar many of the 0551's had - time will tell I suppose. My 0550 has no lockbar stickiness at all while my 0551 did for a while. This may reduce any lock rock development too
* Anything else I may have missed?
Pictures beginning in the next three posts
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The 0551 is further than the 0550 by a good margin but the 0551 probably has a lifetime of wear left. That is where it was when purchased. The 0550 lockup is clearly earlier however I can't say for sure if that was by design or happenstance. With ZT's tight tolerances, I think it just may be their refined direction with regard the the lockup percentage and more forgiving of lock rock or lockbar stickiness with the more acute tang grind angle on the 0550 but Thomas or others with the knowledge would have to comment. I used to be all about super early lockup but that has changed over my years and now I just expect the lockbar and lockup to be spot on and last for years. If a knife does that, I don't care where the lockup is when I buy them. In this case, I'd call the 0550 about 35% and the 0551 at 50%, neither is too early or too late in my book . . .
Both of these knives function extremely well and will provide a relative lifetime of use 
