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[michael hobsonParticipant @michaelhobson77372]

ba 5 to 4

[michael hobsonParticipant @michaelhobson77372]

Hi is it possible to tap out a 5ba thread to 4 ba,without drilling with a 3mm bit first Thanks.

[JasonBModerator @jasonb]

On a shallow through hole yes, I've done it a few times to make one size smaller nuts . But on a blind hole in steel you would need to be very careful, any reason it can't be drilled out first?

J

[JoParticipant @jo]

A 4BA tapping drill is 3.1mm. Unless you use a very sharp taper tap you will not get it to go in the 5BA threaded hole to be able to start the thread.

Jo

[michael hobsonParticipant @michaelhobson77372]

Hi,thanks for the replies,it's on a cylinder of a loco,would be very difficult to probably get a drill in,could get in a 4ba tap unless I used a flexi attachment to the drill but would maybe not get it straight,expect it is made from gun metal Thanks

[julian atkinsParticipant @julianatkins58923]

michael,

the correct answer is no, as im sure you realise as the tapping size for 4BA is smaller than the OD of the 5BA thread plus different TPI.

you will have to go up to 3BA, or 5/32" x 40 tpi.

cheers,

julian

Edited By julian atkins on 28/01/2014 23:11:04

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