Threads topic is not in OCJA . It's in OCJP(Oracle Certified Java SE Professional 1ZO-804)
I would like you to go through this link. You will get all topics cleared about OCJA & OCJP
The OCA SE6 (former SCJA 5/6) was not required for passing SCJP 6 exam. The difference of the exam objectives can be found on the particular web page. For gaining OCP Java 7 you need first pass the exam Java Programmer 1 exam then Programmer 2 exam.