MS35338 Split Lock Washers 1

[daxmann]

We call out MS35338-40 split lock washers on the drawings which are steel, cad plated. For some reason the buyers want to see if MS35338-40M split lock washers are a suitable sub for them. I'm guessing the difference is in the plating but I can't find the spec for the MS35338-40M. Is there a spec or list that shows MS35338-40M as an acceptable sub for MS35338-40 or does anyone have access to the MS35338-40M spec they can share with me? Thank you for the help.

 

[RockEngineer]

According to IHS MS35338 was cancelled in 1996 and replaced with Aerospace standard NASM35338. It is a direct replacement. The M is for zinc plated. I can't give you the copy from IHS due to copyright but it should be available.

 

[Sparweb]

Rather than go to IHS, I usually get MS specs here:

http://quicksearch.dla.mil/

But that copy (valid up to 2002 not 1966) doesn't have a "-40M" so I don't know where your customer gets the "M", unless the NASM conversion of the document introduced it. You may have to buy the spec from IHS, even though it may be just to tell your customer "no".

As an aside... You aren't still relying on these for fastener locking are you?

STF

 

[daxmann]

I am not the designer but seeing as the is a small company I believe it is for locking. Is there an issue?

 

[CoryPad]

faq404-1257

 

[tbuelna]

The "L" rev of the MS35338 standard was replaced by NASM35338, but the part numbering remained the same. The correct part number for the steel washer with cad/zinc plating should still be MS35338-40. I believe your buyer simply included the "M" suffix to indicate the current rev level of the washer standard. Including the rev level on a PO is not normal practice. Instead, standard parts are usually procured to the most current rev level existing.

 

[3DDave]

Split lock-washers are slightly better than air as a retaining device, but they sometimes do some good. In the case of sheet metal parts they increase the amount of screw that is elongated by acting as a spacer. This lowers the sensitivity to small deflections and deformations. But, as for the split, it does nothing. A stack of ordinary flat washers would do as good a job.

 

[tbuelna]

First let me say that I agree with those noting split lock washers are not a good way to secure a threaded fastener. But we should appreciate that daxmann was not the designer that specified the lock washer, nor does he seem to be authorized to implement a design change to remedy the situation. Regarding the question asked in the OP, the correct answer is to direct his purchasing dept to continue using the MS35338-40 part no. specified on the engineering documents to procure the washer. There is no reason to add the "M" suffix. Below is what MS35338 notice 4 states about the PIN for this washer after transitioning to the new NASM35338 standard:

The reason the PIN was not changed when the design standard number changed was precisely for the situation daxmann is facing. Keeping the same PIN did not force companies manufacturing heritage/legacy products to issue engineering changes for every affected standard part.

 

[racookpe1978]

So, what coating do YOU require on the washer - even assuming a split locker washer is going to do anything to hold two pieces of metal together under vibration. Cd plate or Zn coat is going to make a big difference in rust resistance and on the plates you are joining.

 

[tbuelna]

If the engineering documentation calls out MS35338-40, then that means a no.4 carbon steel split type lock washer with either cad or zinc plating is acceptable. That's what the design was qualified with.

I totally agree that using this lock washer seems like a poor choice. But I have also seen split lock washers commonly used with small (ie. no. 4) threaded fasteners for things like electrical connectors.