Symbol: None – Always Implied default condition
Category: Feature of Size
Regardless of Feature Size (RFS) is the default condition of all geometric tolerances by rule #2 of Geometric Dimensioning and Tolerancing and requires no callout. Regardless of feature size simply means that whatever GD&T callout you make, is controlled independently of the size dimension of the part.
This rule can be overridden by Maximum Material Condition or Least Material Condition, which specify the GD&T conditions at the Max or Min size of the part. LMC or MMC must be called out on the drawing specifically though to eliminate the regardless of feature size default.
For simplicity, the definitions of all the GD&T symbols are by default, stated as Regardless of Feature Size. For most geometric symbols besides those that allow maximum material condition, RFS can never be overridden. Regardless of feature size eliminates any potential bonus tolerance, allowing the GD&T tolerances to be more tightly controlled.
Reason for Use:
Since Regardless of feature size is the default condition it is used always and ignored only when specified. It is applied for most part conditions. RFS is always kept where balance is critical and where both sides of the tolerance must be maintained independently of the GD&T callouts.
Regardless of Feature size requires the axis to be measured separately from the size of the hole and cannot be gauged easily. However, there is no bonus tolerance allowed in this condition so the perpendicularity would be much better controlled regardless of the size of the hole.
In the following example, no material modifiers are called out, RFS would be implied and the control for the parts would be like this:
This of course makes sense and follows the normal rules of Geometric Dimensioning and Tolerancing. However if you were to add a Max Material Condition to the drawing, the hole limits are quite different. If you were to control perpendicularity of an axis with MMC, you could control and gauge the part according to Example 2 from our perpendicularity page:
There is now a bonus tolerance that is added to the perpendicularity tolerance to make it larger. With Regardless of feature size this could not happen, as the perpendicularity would have to be the same, regardless of the features size. This is a fairly advanced concept and is better explained in our section on Bonus Tolerances (coming soon).
Measurement/Gauging of Regardless of Feature Size:
Gauging and measurement would apply as normal for this condition for any GD&T symbol. All GD&T callouts must be measured independently from the size of the part.
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How to represent roughness in drawing ???
Surface texture, or roughness, is not part of the ASME Y14.5 compendium. For more information regarding how to specify this on a drawing please reference ASME B46.1-2002. You should note that Pareto Learning LLC and GDandTBasics.com are always working on new content and we’ll likely include a mini-course on this and many other drawing related topics in the future.
Good luck, please feel free to reply back and contribute to the community knowledge base.
Looking for clarification on true position Call out A is Flat Plane Datum, Datum B and C are Cast Hole features.
Our True position box looks like this |.014(M)|A|B(S)|C(S)|
The Customer has stated we get no hole position bonus with this MMC – Can you help?
The print you’re looking at appears to be using the 1982 standard, but this doesn’t matter. The inclusion of the (S) or not just means that the datum references are to be considered at Regardless of Feature Size. Later revisions of the standard discontinued the use of (S) as it was never a requirement to begin with. The default is always RFS. Anyway, what really matters here is the inclusion of the (M) or Maximum Material Condition modifier in the feature control frame. Anytime MMC or LMC is called out you always are permitted a ‘bonus’ tolerance.
Without additional information I can’t really get to what they are getting at, but I do believe they are wrong. I hope this helps, good luck.
Please could you add a separate page for “Bonus Tolerance” for both MMC & LMC with 2-3 examples for each.
It’s a humble request.
Our team is hard at work on our Advanced GD&T course right now. We do plan on circling back and adding valuable content to the website in the future though. Thanks for checking in!
What are the advantages of using RFS instead of MMC? Will there be a significant cost difference between RFS and MMC?
It’s not so much about advantages as much as it is application based. Each modifier (or lack thereof) provides its own benefits. It seems as though you are familiar with the concept of MMC but you should take note of when to use LMC and RFS as well.
MMC is used when you have a clearance application, when you’re trying to get a hole to provide clearance for a bolted joint assembly.
LMC is used when you are trying to control a wall thickness and ensure that you maintain a minimum stock to prevent breakthrough. LMC isn’t as commonly used as MMC.
RFS is used when the size of the feature has no direct impact on the location. An example of this would be a pin or bushing that is press fit. Regardless of the size of the hole the bushing will self center in the press fit hole, having additional bonus tolerance doesn’t help here.
I hope this helps. We go into further detail on the how and when to use each modifier in our GD&T Basic Course! Take a look, maybe it’s a good fit for you.
I have some doubts regarding the perpendicularity at RFS. Let´s say I want to design my pin to fit the hole showed above. Then I should consider the diameter of the pin to be the dimension of the part envelope as maximum, is it correct?. In this example the diameter is 10 +- 0.1, and he geometric tolerance is 0.2, then it means that the pin that will fit in that hole must have 10-.1-.2= 9.7 mm as maximum assuming it is perfectly perpendicular oriented, is it correct?
I believe you are confusing the issue. When there is neither an MMC or LMC symbol next to the tolerance value you get no ‘bonus’ tolerance. You simply get the tolerance value as listed in the feature control frame regardless of the size that the feature is produced at. The goal here is functional assembly of your parts. For a hole in a part, it should make sense that as your hole increases in diameter you can also accommodate a greater tolerance and still get your part to assemble.
Perpendicularity is like position’s little brother. They both control the perpendicularity of a hole (in this example) relative to a datum. When you have perpendicularity called out for a hole, your tolerance zone is a cylinder of size (tolerance value) that is perfectly perpendicular to your datum surface. The axis of the hole must lie entirely within the tolerance zone for your part to be accepted by inspection. The tighter the tolerance zone the straighter the hole must be.
When RFS is specified you are in effect stating that you don’t care what size the hole is, the tolerance (and hence the perpendicularity) of the hole stays the same. It’s for this reason that you frequently see perpendicularity as a refinement of position. Here you would use the larger tolerance zone to locate your hole and your perpendicularity call-out to restrict the tilt of the whole to a tighter degree. It all really depends on application.
I hope this helps. If you have further questions, please don’t hesitate to ask.
What is CFD-CPD means as I saw in the drawing with this call out
In my opinion, R F S condition is applicable in case of critical fitments (fitments involving critical demands like wear control, leakage prevention, smoothness at precision motion etc.) Other conditions ( MMC, LMC) are applicable for non-critical fitments (fitments only meant for fitments)
Furthermore, a no symbol for RFS may mean that the designer has forgotten to put some required symbol. I feel there has to be a symbol for RFS.
In revisions to the standard earlier than 1994, the symbol to indicate that the tolerance was to be taken at RFS was an S enclosed in a circle. This could appear after the tolerance or after the datum (as applicable). It was done away with in the 1994 revision of the standard as it was felt to be redundant/unnecessary and some of the governing definitions/rules had changed. At any rate, as the current standard (2009) stands if the designer wants the tolerance to applicable at any feature size within limit of size NO symbol is added after the tolerance in the feature control frame.
As to why a designer might want this: Here are some handy rules of thumb as to when to use which material condition
MMC – Assembly, locations of non-critical fitments (as you state)
LMC – Minimum wall thickness or minimum distance between featuers, alignment
RFS – Control of symmetrical relationships, centering and alignment
I hope this helps.
can anyone tell me what does an encircled s implies in gd&t,,,,,?
Sure thing. The circle S is a now discontinued practice that just means that the tolerance or the datum is to be taken at regardless of feature size. This symbol was phased out in the 1994 standard because it was deemed redundant with not putting anything there at all. The only datum modifiers allowed anymore are circle M (MMC) and circle L (LMC). There are several tolerance zone modifiers in addition to MMC/LMC. Just know that if you come across the circle S, take your pen and cross right through it and it has the same meaning.
Glad I could help.
how it comes 4.4 mm perpendicular limit?
yes, you right!
what is formula of MMC?
There are a few formulas associated but the main one is to calculate your virtual condition. This will be:
For an external feature (pin/boss)- Your largest size (MMC) + your geometric tolerance
For an internal feature (hole) – Your smallest size (MMC) – your geometric tolerance.
MMC (For Shaft)= Maxi.Dia of shaft
(For Hole)= Mini.Dia.of Hole
Santosh / Sami –
You are correct! Another way to think of it is that MMC is the condition that will result in the part being the heaviest, whether this is an internal or external feature. As you’ve pointed out MMC for a hole is the minimum diameter and for a shaft it is the maximum diameter. Keep the information flowing guys!
It is more clear, if iy is explained with examples (Two to Three at least)
The drawing illustration for RFS is actually MMC , and visa versa. I think they were occidentally swapped.
Thanks for the notice! Should be changed now.
how part would be inspected for RFS?
It depends on what you are measuring for. RFS is the default condition of GD&T for all the symbols. It simply means that you need to hold whatever geometric tolerance as specified. You do not get any bonus tolerance if the size of your part becomes favorable.
Why does it say Hole Φ = 10.1 +/-0.1? Should it be Φ = 10.0 +/- 0.1?
Yes you are correct – thanks for letting us know about the mistake!
The problem for mmc is incorrect. The (internal feature) hole is MMC at 9.9 and at this size the tolerance zone is 0.2
The (internal feature) hole is LMC at 10.1 and at this size the tolerance zone is 0.4.
You are right! The values were reversed somehow from the perpendicularity page. We will change this right away.
Thank you for pointing this out!
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