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BSF vs SAE

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drooartz

drooartz

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I'm still a bit confused about these fasteners (maybe I'm just a bit slow, it's entirely possible). In doing some reading on ye olde internet, I keep reading that SAE (also called UNF) is not the same as BSF. Something about the SAE thread pitch is 60 degrees, and the BSF is 55 degrees.

https://www.jag-lovers.org/xk-lovers/library/whitworth_system.html
https://www.enginehistory.org/british_fasteners.htm

Now, folks here who I trust completely on subjects LBC have written (or I have read them to have written) that they are interchangeable. Or that our lovely little Bugeyes came with SAE threads.

I'm confusled...
 
and to add a little more to your reading BCF search results

basically, they are NOT the same, there may be one or two sizes the will sorta fit. But it is not recommended to mix and match.

mark
 
Maybe they so close it makes no difference but SAE works fine, check it out for yourself. Buy one bolt and one nut and check.
 
I think the spridgets were mostly SAE.
 
Bugeyes are old enough (built in the late 50s) that they should still be BSF. I didn't think the British ever went to UNF/SAE, they went to metric instead.

Some of my reading says that the UNF may seem to fit, but really doesn't. To quote the Engine History site listed above:

[ QUOTE ]
Another area that causes confusion is the fact that some BSW or BSF nuts can be screwed on UNF or UNC bolts and vice-versa. Under NO circumstances should this practice even be considered. Most of the coarse threads share the same threads per inch which means BSW nuts can be screwed onto UNC bolts and vice-versa. The exception to this being ½ inch -- ½ inch BSW is 12 threads per inch and ½ inch UNC is 13 threads per inch. Again, it must be emphasized that this practice should not be a consideration. Whitworth and UNC/UNF thread forms differ greatly, the primarily one being the thread angle (see illustrations). BSW and BSF feature a 55 degree thread angle (47 ½ degrees for BA) and UNC/UNF threads feature a 60 degree thread angle. Consequently, if these fasteners are interchanged, considerable loss of holding force, fatigue resistance and strength will result.

[/ QUOTE ]

(This site could be up in the night as well, that's why I'm trying to clarify for myself)

Not trying to start any holy wars, just trying to make sure that I am understanding things correctly. I'm lucky in that I don't need all the bolts for my car, just a few odd bits here and there. For such a small quantity, I'm not concerned about paying a premium to Moss or whomever.
 
SAE slips into the captured nuts nice as you please in all cases where fine thread is used in the body anyway. I can put them in with my fingers.
 
I absolutely believe you, Jack. That's why I'm confused. The article seems to say that they will go in, but that it is somehow not good. Not even quite sure I know what a thread angle is. Should have paid more attention in Physics classes in college, I guess.

I'll have more of these questions, since I'm back into learning mode having recently dropped out of money mode.
 
As I foggily recall from another thread, Spridgets are mostly SAE save for a few parts on the early cars (ie Carbs and shocks) which had been in manufacture as BSF for some time before the spridget hit the scene.

But I am frequently wrong about such things.
 
Hi Drew,
To quote from your second source again:
----------------------------------------
Another area that causes confusion is the fact that some BSW or BSF nuts can be screwed on UNF or UNC bolts and vice-versa. Under NO circumstances should this practice even be considered. Most of the coarse threads share the same threads per inch which means BSW nuts can be screwed onto UNC bolts and vice-versa. The exception to this being ½ inch -- ½ inch BSW is 12 threads per inch and ½ inch UNC is 13 threads per inch. Again, it must be emphasized that this practice should not be a consideration. Whitworth and UNC/UNF thread forms differ greatly, the primarily one being the thread angle (see illustrations). BSW and BSF feature a 55 degree thread angle (47 ½ degrees for BA) and UNC/UNF threads feature a 60 degree thread angle. Consequently, if these fasteners are interchanged, considerable loss of holding force, fatigue resistance and strength will result. Unfortunately, this author has seen examples of mechanics -- unaware the these subtleties -- mixing fasteners at will -- gee, if it screws on it must be okay..!! (Scary thought).
--------------------------------------
Especially note;
"considerable loss of holding force, fatigue resistance and strength will result."

Translation - if the holding power & strength of the fastener is is not critical the two thread forms could possibly be mixed. If the fastener IS critical, don't mix the two thread forms.
D
 
[ QUOTE ]
SAE slips into the captured nuts nice as you please in all cases where fine thread is used in the body anyway. I can put them in with my fingers.

[/ QUOTE ]
They slip in so easily because they are a much looser fit than intended. If a loose fit (read weak) is acceptable, go ahead. Just don't do it on critical fasteners such as suspension, structural, engine, etc.
D
 
I run a tap thru any captive nut, most captives on a Sprite are for non moving parts anyway. pedal box, clips, pipes, etc.
If you are replacing a bolt, put a new nut on it.
Caliper bolts are special, use what came on the car.
I have chased most threads with my UNF tap set and put the original bolts back in like the shock mounts, never a problem.
The fuel system is still Whitworth but a 10/24 on a boogered carb float bowl tread will save the day.
I have been using SAE fine US made (not chinese) hardware for 30 years. I have restored over a dozen Sprites and nothing ever fell off. Well, nothing that had a new nut or bolt that is. Lots of stuff falls off these cars I even have a sticker that says "All Parts Falling Off This Car Are Of The Finest English Workmanship" /ubbthreads/images/graemlins/wink.gif
 
Okay, I've been reading some more, this time in my trusty Horler book. Morris and Trevor seem to have hit it right. In a quick read through the Bugeye section, a number of bolt sizes are mentioned for various things, and they were all listed as UNF threads. So there you have it. I was wrong that the Brits didn't use UNF. It seems they certainly did.

BSF and UNF are not the same, but we're dealing with UNF threads here. It's been an educational evening for me, that's for sure!
 
Whew, I was about to go dig around for the two BSF taps I own and test your theory. I've never had any problems using UNF, even on things that required significant torque.
 
Very few Whitworth fasteners were used on our LBC's designed after about '55~'56. Mostly SAE NF ("fine" thread) and a few NC ("coarse" thread) types. Shock filler bungs and carbs, as Morris said.

You're really gettin' into the piddly-bits, Drew! Soon you will be a walking Frogeye encyclopedia! /ubbthreads/images/graemlins/wink.gif
 
Thanks DR. I was scratching my head on this one since every LBC I've worked on (all post 1960) clearly used a mess of 1/4-28 and 3/8-24 fasteners. The only odd stuff I keep coming across are the BA series taps used on things like gauges.
 
BTW: I read your tretise on guages yesterday. Great stuff!
 
Well Doc, I'm back in education mode like I was when I was first looking for a LBC. I'm out of funding for the foreseeable future, so instead of parts and repairs, I'm gathering information. Costs less, and is quite valuable! /ubbthreads/images/graemlins/grin.gif
 
Hello all,

UNF\UNC (SAE) are normal threads used on British cars of the sixties onward (and before) One car I know uses Whitworth form is the Morris Minor but only for body and suspension parts, engine and gearbox are SAE. Interestingly Morris bought out a French Engine manufacturer (not sure exactly when 30's or 40's?), retained the metric thread form but used Whitworth sized hexagons on the fastners, how is that for confusion?

Alec
 
Thank goodness Bugeye fastners are available all over the place now that I know what I am looking at/for.

Have been useing all Stainless Steel but for suspension and shocks and such. I dislike rust with a pasion.
 
Yup, Jack. Me too. Stainless ROCKS! I even put "NutZerts" in the doors/panels to attach the interior trim panels with 6-32 machine screws so there will NEVER be another rusty trim screw again. Stainless "cup washers" too.
 
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