Originally Posted by
manolain
My main question here is (sorry I did not get this very clear from your post): I will land from my international flight, clear customs, and get my baggage, so I head to Terminal 1.
But on this way, do I have to pass security again? Will this security prevent me to get my big checked luggage into the area where lockers are?
Unfortunately, yes and probably yes. After landing in T3 and clearing customs/immigration, you will be outside of security.
While TSA generally doesn't care how big a carry-on bag is (since that's up to the airlines to enforce), the bag must be able to go through the security screening machine. I have no idea exactly how big a bag can fit through, but based on my recollections, the width will probably be a problem for bigger check-in bags.
Ironically, the "jumbo" size lockers at LAS can almost accomodate any check-in under BA limits - the lockers have a stated capacity of 35" x 31" x 19" as per
https://www.mccarran.com/Find/Facilities.aspx