(Why yes, I DO love pirates! How did you know?)
The latches I use are from Tandy Leather, I found some at my local leather shop, and then a little cheaper online. You'll need the latch, plus rivets to match. Mine are in the antique nickel.
(My latest hardware order, now I need to make wallets to use them up!)
The latches are the 'small' size, which is about 1 1/4"
Rivets are the small size (probaby 1/4", but I forgot to measure) and come in a pack with a lot. If you buy your latch in a shop, you can always ask for the rivets and they'll get you the right size and the matching setter. Each fastener takes 4 rivets (assuming you don't screw up!) but I've seen some places selling the rivets and latches together. Rivets have 2 parts, a cap and a long part. I'm sure they have real names, but I like to call them the 'pokey through' and 'front' parts. You'll also need a rivet tool, to set them, a hammer, and something to hammer on. I don't suggest your table unless it's super sturdy and you don't mind tiny round marks in it. I use a piece of flagstone that was left over from working on the patio. I've also used our front (concrete) steps in an emergency, or my self healing mat, but that left a mark on the mat, so back to the rock I went!
(My lovely rock. That I constantly stub my toes on because I never pick it up)
To install the latch, first make the flap (NCW pattern). Instead of cutting out for the twist lock, you will need to find the center of the flap and position the the loopy part of the latch so that the loop is off the edge, and it is centered on the flap.
(This is actually finished, but gives you the placement idea)
Make a mark with a pen for the 2 holes. Remove the latch and punch out the holes. I found my husband's leather punch on the smallest hole is perfect, but before I had that bright idea, I was using the poky tool from my KAMsnaps and my seam ripper to try to make the holes, then forcing the pokey piece of the rivet through the hole while cursing and losing feeling in my fingers. I much prefer the punch.
(awesome tool for hole punching through many layers)
Poke the longer 'pokey' side of the rivets through from the BACK side, place the latch on top, and make sure it fits. Try to center the rivets in the holes.
If you want, now is the time to put fray stop around the outside of the rivets to give a little more strength to the fabric. Give it a minute to dry, then the fun starts. Put the latch back on, and swing the hook out of the way. First, place a cap (front) piece of the rivet on top of the sticking up part. This is the nice looking part. Place the rounded end of the tool on top of the cap, try to hold it straight, and then give it a few good whacks. You're bending metal, so don't hold back! Of course, if you are pretty strong, you might make a few scratches if you keep going once it is flush. I like to hit it enough to catch (if you pull gently up on the cap, it won't come off), but not all the way, then do the other one. Once they are both attached and in the right place, go back and make sure the first one is secure. You shouldn't be able to wiggle the latch at all and there shouldn't be any gaps between the fabric and the latch. The backs of the rivets will be slightly recessed into the fabric.
(Back of flap)
(This is actually finished, but it gives a visual of where the latch will go)
(You can see the square stitching on the bottom, make sure you aren't too close to that, or you will have a hard time getting the wallet to close. Trust me, I tested that out.)
(Scuff marks on piece from going to town on the rivets. Good news is they won't fall out! I hope anyway...)
(Inside of the clutch, front. Note that they rivets don't show through, make sure you are only making the hole through the front fabric)
Center the bottom of the latch on that flap. Holding it in place, test with the top to make sure it looks right. Sometimes I nudge it to one side or the other to help it line up better. Mark the holes for the bottom latch. If you haven't put the square of interfacing in yet, you can put it right under the marks and it will give you extra stability/security. Carefully make the holes for the rivets. I use the leather punch and squish the fabric down a little so it can reach. Stick the pokey side of the rivets through the holes (inside to outside) and double check the alignment. (I don't know if you could really fix it at that point...) Place the bottom latch piece on the rivets, and attach the first cap in the same way as previously (leave one slightly loose until they are both on, so you can wiggle it straight). Once you have the piece attached, top stitch your opening shut and finish the clutch.
Sometimes your rivets won't seem to catch no matter how much you beat on them. Usually this happens if you aren't square on top of them, or hit slightly to an angle and they get bent. If you pull them out, you'll see they look like they were run over by a car. It's hard to get a good picture of this, but trust me when I say that if you held these in your hand, you'd see right away why they don't work. I've done this a few times, and the best thing to do is toss them and start with new rivets.
(I meant to do this, so I could have an example. Totally not an accident.)
I hope that gives you a good idea of how to install the swing latch, if anyone has any questions, I'll do my best to clarify! Good Luck!