Civic Forumz - Honda Civic Forum - Honda Part Number Definition...

Honda/Acura part numbers are broken down like this.

I'll use the EX front brake upgrade knuckle as an example. The part number for the EX R.side knuckle is ??.51210-SH3-306 The part number for a R.side Civic Si knuckle is ?.51210-SH3-040

Function Number - 51 xxx-xxx-xxx(xx)
Honda numbers are divided up into functional sections - fuel system, brakes, chassis, etc. Each section is assigned a Function Number. The chassis section has a function number 51. That's where the knuckle is. The chassis.

Component Number - 51210-xxx-xxx(xx)
This number designates a particular part number within a functional section. In other words, if you have a steering knuckle, the function number is 51 (chassis) and the three digit Component Number for a '90, '91 EX sedan is 210. So all put together, a right side steering knuckle on anything honda/acura is 51210.

Product Number - 51210-SH3-xxx(xx)
The Product Number designates the original use of the part, the type of part, and the class of part. This number can be either alpha, numeric, or both. Here, it's both - SH3. This is the number you want to look at when you are questioning the fit of a part from another car (or motorcycle, as I found a lot of!). Another prime example of using the center digits is, when I was looking for rear disc brake donor vehicles. 2nd gen Integra's happen to have the same trailing arm center digit as the Civic/CRX - also SH3. Same scenario for the rear calipers on '90, '91 CRX's and 2nd gen Integra's. That is SK7.

Classification Number - 51210-SH3-306(xx)
This designates a classification for the part, such as general parts, export area, special service, or manufactured somewhere other than American Honda. When you get to this number, and it starts to differ, it's a good idea to physically get the parts side by side and look at 'em to see what's different. In the case of the knuckle, I found the 306 and the 040 difference mean that the caliper mounting ears on the knuckle are further (in radius) from the center of the hub. The classification number does not always mean that parts won't interchange, sometimes it's just in the manufacture of the unit.

Special Number - 51210-SH3-306(xx)
This is an optional number that is used for further designation of painted parts, finish (polished or whatever), or calipers for instance, RM at the end means re-manufactured.