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03-02-2010, 4:50 AM roadster5580 Joined on 01-18-2008 Atlanta, GA Posts 326 Maybe Some Help With Metric Fasteners I bought a new set of metric tap&dies yesterday.  If you work on bikes a lot, you're eventually going to need a set.  While I'm not a machinist.  I've worked on enough "metric" bikes over the years to get a pretty good understanding of metric hardware.  Don't even bother asking the guy at the local Lowes or Home Depot about metric hardware, they simply don't know.  With that thought in mind, here are a few points I've picked up over the years that might help a few guys just starting out to understand metric fasteners a little better. Like SAE fasteners, metric fasteners are also graded by bolt strength.  While SAE bolts are graded by a / mark on the top of the bolt, metric bolts use a numbering system.  The lowest grade metric bolts are 8.8.  These bolts are marked 8.8, or with a single dot, or no marking at all.  These are the usual "mounting" bolts for case covers, seats, tanks, etc.  "Structural" nuts and bolts are usually 10.9 steel.  "Structural" fasteners would be the head bolts, rod/main bolts, frame/suspension bolts.  Racers generally use 12.9 bolts on their "structural" fasteners.  These are the highest strength metric fasteners and are about twice the load strength and half again the yield strength as 8.8 metric fasteners. You have to be careful when identifying the sizes of metric nuts and bolts, especially the thread pitch.  There is only one "metric coarse" pitch thread and this is the standard thread pitch used on most Japanese bikes.  Unlike SAE nuts and bolts - metric fasteners can have a number of "fine" thread pitches and there are a few "extra course" pitches out there as well.  For example, a M5 bolt (5mm diameter) will have a standard "coarse" pitch of 0.80 - but ISO standards also use M5 x 0.5, M5 x 0.75, M5 x 0.90 nuts an bolts as well.  You'll see these other pitches called "extra coarse" (EC) or "extra fine" (EF).  In addition, you"ll some times come across a "metric fine" (MF) fasteners.  Since these non-standard pitches differ by only 0.05mm, even a thread gauge comparison can fool you. As I said, most nuts and bolts on a Japanese bike use "metric coarse" as the standard pitch, with some fine and odd pitches thrown in just to confuse the hell out of you. I've come to the conclusion that German bikes must use German metric standard (not ISO).  You see a lot more fine pitched threads on German bikes.  With that said, here are the common "metric coarse" bolt/thread combinations I've see on most Japanese bikes along with the tap drill sizes in both MM and SAE: SIZE           PITCH                       MM TAP DRILL                  INCH              SAE TAP DRILL M5                0.80                           4.20 MM                                .165                          #78 M6                1.0                             5.00 MM                                .196"                         #76    M8                1.25                           6.80 MM                                .267"                         #71  M10              1.5                             8.50 MM                                .334"                         #66 M12              1.75                           10.20 MM                              .401"                         #60 M14              2.0                             12.00 MM                              .472"                         3/64 M16              2.0                             14.00 MM                              .551"                         #54 M18              2.5                             15.50 MM                              .610"                         #53 M20              2.5                             17.50 MM                              .688"                         #51 M22              2.5                             19.50 MM                              .767"                         #48 M24              3.0                             21.00 MM                              .826"                         #45 Anybody else want to share their experiences with metric fasteners?  BTW - Quite worrying about the Chinese taking over the world for awhile, they can't machine threads for crap.    Report

03-02-2010, 6:52 AM NoXi Joined on 08-04-2008 UND Posts 308 Re: Maybe Some Help With Metric Fasteners thanks for the info! i knew SAE but i always thought the strongest metric were 8.8, i know better now :D 82 gl 500 silverwing (dizzy) 82 gl 500 interstate (the brown streak) 81 susuki gs550 (suzy (chopper)) 99 R6 chop project (ace of speed) Tell me the location and velocity of every particle in the universe and ill tell you your future    Report

03-02-2010, 7:57 AM dfritz08 Joined on 10-01-2009 Marion, Iowa Posts 156 Re: Maybe Some Help With Metric Fasteners i would say this info would be a good link in the quick reference section, i am bound to use this info numerous times in the next few months just my opinion -Fritz 1980 cx500d 1981 cx500c (getting bobbed)    Report

03-02-2010, 2:58 PM Sams GL 650 Joined on 02-17-2010 Annville PA (USA) Posts 191 Re: Maybe Some Help With Metric Fasteners Thats good info Roadster, thanks. sam Bikes: 2002 Kawasaki Vulcan 1983 Honda GL 650 1 st Bike Honda CL 175 (1974) Age 52    Report

03-06-2010, 6:28 AM rlcorn64jh Joined on 03-26-2007 Brookfield, CT Posts 24 Re: Maybe Some Help With Metric Fasteners Folks, I bought a tap and die set from Harbor Freight for a silly amount of money.  They were so "cheap" that I bought two of them.  When working with 30-year old fasterners, getting the bolts back in can be difficult, so I re-tap the holes and put the bolts through the die to clean the threads well enough to be able to insert and tighten the bolts by hand until the last few turns. If you have to drill out just one tight bolt that broke off, you'll smarten up as I did.  PB Blaster helps get the old bolts out without breaking them most times. I found a great hardware store in Cheshire, CT that handles a wide range of metric screws and bolts.  They even have a limited supply of chrome bolts, though they are mostly SAE not metric.  I've replaced dozens of carb screws and the screw that holds in the tach cable I've replaced with a hex-head for future ease of removal.  Headlight screws look nicer if they are new, so I generally replace those.  When I shop, I take metric nuts with me to try the replacement screws and bolts.  I have a selection of bolts and screws in little plastic bags marked for size and length complete with a new nut for testing future bolts.  I also mark the bags as to what area of the bike they might be used for:   headlight, carbs, seat, tach retaining bolt, etc.  This is not anal retentive stuff if you have 14 bikes, this is efficiency. Russ Cornelius -o- One 1977 Honda 360 nearing complete repair 13 cx500's 1978 - 1981 7 run so far    Report

03-08-2010, 5:50 PM roundman72 Joined on 03-24-2009 Laporte Indiana Posts 393 Re: Maybe Some Help With Metric Fasteners the only thing i will say about the cheap stuff (taps and dies) is you get what you pay for.  i have a cheap craftmans set for the odd sizes but the common ones i bought good ones from a tool and die store.  i find that the tolerances (there is actually a rating for the thread tightness i think i bought g3, been a while)  and find that they work a lot better.  i use the split dies and you can control how much you clean up.  And i have never broken a good tap using it correctly.  but due to cost i only have the real common ones and suffer with the other ones when i have to use them. 82 gl500I 82 xs650 70 cl450 (restoring) 74 cl450 (non runner) 00 Moto Guzzi Jackal (ended up selling)    Report

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