A:AnswerI would be concerned about mounting a Play 3 with these. I've got a pair of Play 1's mounted as rear speakers and while they are doing the job, I'd be weary about anything larger. Check the weight of a Play 3 against the specs on the mount too be sure.
A:AnswerNot sure what mounting holes you have but brackets are rated for speakers up to 8 lbs. The come with several mounting options including a single 1/4-20 (which my Polk RM2300's use) or a two hole bracket. See attached pictures I took from the installation instructions.
A:AnswerThese mounts are very robust, if you screw them tightly into a wood beam/brick wall, they will hold heavy shelf speakers. I do not recommend screwing them to a dry wall for heavy speakers (more than 5 lbs.).
A:AnswerWhile I don't know specifically about you Logitech system, I do know it needed a specific fine thread screw to go into my Sony system which these had. As well as many other different screw sizes and lengths.