Threads: UNF-3A vs UNF-3B

[markocosic]

Residing in England and so not being used to English measurements...

Is this correct?

UNF-3A - "male UNF thread"
UNF-3B - "female UNF thread"

UNJF - "rolled UNF thread"

Is it safe to put a male UNJF threaded bolt into a female UNF thread? (ie - screw an AN bolt into a hole I've cut using a tap)

As far as I can see there'd just be some extra clearance as the tapped hole would have "\/\/\" where the bolt has "unununun" because it was rolled rather than cut.

[TG]

UNJ has a slightly different profile from UN in that there are fillets in the roots as opposed to flat roots. THis makes for a stronger thread. UNJ is the latest type of thread to be standardized, there was a UNR thread before that that also had root fillets, although of other sizes.

Rolling has only to do with manufacturing and nothing of the thread profile. You want rolled threads because of grain refinement at the surface.

[Frank]

machinery's handbook

"Thread Classes."”Thread classes are distinguished from each other by the amounts of
tolerance and allowance. Classes identified by a numeral followed by the letters A and B
are derived from certain Unified formulas (not shown here) in which the pitch diameter tolerances
are based on increments of the basic major (nominal) diameter, the pitch, and the
length of engagement. These formulas and the class identification or symbols apply to all
of the Unified threads.
Classes 1A, 2A, and 3A apply to external threads only, and Classes 1B, 2B, and 3B apply
to internal threads only. The disposition of the tolerances, allowances, and crest clearances
for the various classes is illustrated on pages"...

"Standard Tap Marking: NF
Product Thread Designation: UNJF
Fine pitch series, with rounded root of radius 0.15011P to 0.18042P (ext. thd. only)"

http://assist.daps.dla.mil/quicksearch/basic_profile.cfm?ident_number=7373

revision C

[markocosic]

Thank you both!

Essentially the thinking on A/B was correct, the classes 1/2/3 are all tolerancing, and if I thread a male UNJF thread into a female UNF thread I'll knock the peaks off the thread profile the first time that it goes in - if they were left intact by the tap in the first place that is.

[Pravin]

UNF -1B >>Nut
UNJF-3A>>>Bolt

Is this correct combination ?

[Drew Price]

Originally posted by Pravin:
UNF -1B >>Nut
UNJF-3A>>>Bolt

Is this correct combination ?


No.... well... sort of....


UNJF-3A = UNJF standardized tolerance class 3 fit (medium-tight fit) bolt.

UNF-1B = UNF standardized tolerance class 1 fit (LOOSE fit) nut.

Do NOT thread a class 3 bolt into a class 1 nut, the threads will not fit together 'snug.'


Read this, remove the spaces.

h t t p://en.wikipedia.org/wiki/Unified_Thread_Standard#Tolerance_classes



Drew