The best approach is using an alloy that contains more lead then tin as the melting point will be lower thus less chance of buring a hole through the lead pipe.Lead wiping is the best approach
They make both kinds. Just make sure it fits snug before you glue it.
Answer.
there are several types a 3x4 fits over 3" and inside 4" but there are ones that will go over 4" and inside...