BMW Bolt/Screw Spec Question

Theodore · 06-10-2017, 11:58 AM

What does the "U1" represent in BMW bolt/screw designation?

Here is an example, this is for the Torx screw that holds down the throttle actuators, BMW part # 07129905558. The description on nearly every website for this screw reads:

M6X25-U1

A photo borrowed from ECSTuning:

And here is it is on RealOEM with the same description, M6X25-U1.

I'm usually pretty good at Google searches, but this time I can't find an answer. The U1 is where BMW usually lists the "grade" or strength of the bolt (often 8.8, 10.9 or 12.2), is it possible this represents some sort of grade? I'm also wondering if it could it be a BMW code for "one time use," "update 1" as in a newer version of the bolt, or something else entirely?

admranger · 06-10-2017, 09:22 PM

What's the BMW part number?

It's likely 10 Nm dry.

Theodore · 06-10-2017, 10:48 PM

It's 07129905558

admranger · 06-11-2017, 03:42 PM

Quote:

Originally Posted by Theodore

It's 07129905558

The U1 is not grade of bolt like 8.8 or 10.9 as far as I can tell. I saw a U0-8.8 when I was noodling around realoem. Must be something else.

You should be good at 10Nm based on a google search for M6 torque specs.

Theodore · 06-11-2017, 09:15 PM

Thanks. After a lot more searching, I still can't find an official definition, but I see a pattern in all the U0, U1, and U2 designations I could find: They each have an incorporated washer, the smallest washers (in relation to the screw/bolt head size) tend to have the U0 designation and the largest washers tend to have the U2, with U1 used for washers in between the two extremes. Maybe that's all it is and they simply leave off the screw/bolt grade in many of the descriptions.

dparm · 06-12-2017, 05:54 PM

Grade 8.8 bolts are already insanely strong. I suspect they don't bother including the grade in most of the part numbers because they're holding together piddly shit that isn't subject to immense forces. Do you really need a grade 8.8 bolt to hold an interior trim piece? No.

For stuff like suspension, brakes, etc., then yes, I would think they specify the grade.

06-10-2017, 11:58 AM	#1
Theodore Lieutenant 669 Rep 412 Posts Drives: 2011.5 E92 M3 Join Date: Oct 2015 Location: Tampa Bay, FL iTrader: (6)	BMW Bolt/Screw Spec Question What does the "U1" represent in BMW bolt/screw designation? Here is an example, this is for the Torx screw that holds down the throttle actuators, BMW part # 07129905558. The description on nearly every website for this screw reads: M6X25-U1 A photo borrowed from ECSTuning: And here is it is on RealOEM with the same description, M6X25-U1. I'm usually pretty good at Google searches, but this time I can't find an answer. The U1 is where BMW usually lists the "grade" or strength of the bolt (often 8.8, 10.9 or 12.2), is it possible this represents some sort of grade? I'm also wondering if it could it be a BMW code for "one time use," "update 1" as in a newer version of the bolt, or something else entirely? Last edited by Theodore; 06-11-2017 at 01:25 PM..
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06-10-2017, 09:22 PM	#2
admranger Retired Curmudgeon 2985 Rep 4,047 Posts Drives: ‘19 X3M40i, ‘18 m550i Join Date: May 2011 Location: Las Vegas, NV iTrader: (1)	What's the BMW part number? It's likely 10 Nm dry. __________________ '19 X3 M40 Carbon Black/Oyster, '23 Jeep Grand Cherokee L Summit, Past BMWs: '18 M550i, '18 330 GT, '16 X5 40e, '11 E90M3, '06 X5 4.4, '03 330i ZHP, '02 M3, '97 Z3 2.8, '95 M3 (2x), '94 530i (manual), '92 525i (manual), '88 M3, '87 325iS
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06-10-2017, 10:48 PM	#3
Theodore Lieutenant 669 Rep 412 Posts Drives: 2011.5 E92 M3 Join Date: Oct 2015 Location: Tampa Bay, FL iTrader: (6)	It's 07129905558 __________________ What I Wish I Knew When I First Bought My E9X M3 Can Be Found Here E9X M3 Exact Original Equipment (OE) Equivalent Parts Can Be Found Here E9X M3 Common Torque Specs Can Be Found Here E9X M3 "Factory" Tools Can Be Found Here
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06-11-2017, 09:15 PM	#5
Theodore Lieutenant 669 Rep 412 Posts Drives: 2011.5 E92 M3 Join Date: Oct 2015 Location: Tampa Bay, FL iTrader: (6)	Thanks. After a lot more searching, I still can't find an official definition, but I see a pattern in all the U0, U1, and U2 designations I could find: They each have an incorporated washer, the smallest washers (in relation to the screw/bolt head size) tend to have the U0 designation and the largest washers tend to have the U2, with U1 used for washers in between the two extremes. Maybe that's all it is and they simply leave off the screw/bolt grade in many of the descriptions. __________________ What I Wish I Knew When I First Bought My E9X M3 Can Be Found Here E9X M3 Exact Original Equipment (OE) Equivalent Parts Can Be Found Here E9X M3 Common Torque Specs Can Be Found Here E9X M3 "Factory" Tools Can Be Found Here Last edited by Theodore; 06-11-2017 at 09:20 PM..
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06-12-2017, 05:54 PM	#6
dparm Stop the hate, get a V8 3850 Rep 8,625 Posts Drives: C7 Corvette GS, AMG C63 S Join Date: Jun 2013 Location: Frisco, TX iTrader: (1)	Grade 8.8 bolts are already insanely strong. I suspect they don't bother including the grade in most of the part numbers because they're holding together piddly shit that isn't subject to immense forces. Do you really need a grade 8.8 bolt to hold an interior trim piece? No. For stuff like suspension, brakes, etc., then yes, I would think they specify the grade. __________________ Now: 2017 Corvette Grand Sport, 2021 AMG C63 S sedan Past: 2011.5 M3 sedan ZCP
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