First of all, the principle of this type of strap/sling, is to allow the camera to move freely and quickly from your side/hip to your face without tugging at your torso. It's also much more comfortable to wear your strap diagonally over your shoulder than just over your head.
The most important part is the base plate. I bought a couple to try out on ebay for under $10 each and they are both fine. You ultimately want a plate that will screw into the tripod mount under your camera firmly and is strong. I recommend finding one that has a tripod mount on it so you don't have to remove it from the camera when you need to use a tripod. It also needs to have a loop or ring attachment so it can connect to the strap.
Next you need rings and clips to attach the base plate to the strap. There are a variety of types of rings and clips that will do the job but most importantly it has to move freely on the strap. One word of caution - some parts are cheap and strong - others are not! I did buy a cheap speed/quick strap on eBay with a clip (similar to this one pictured) and it broke! Yes - at the worst time! Incidentally I wouldn't use the one pictured either - although strong, I feel the lever to open the clip sticks out to much and it could accidentally open up - not worth the risk. I use clips that screw closed - safe and secure.
The sling or strap should be comfortable on your shoulder and the narrower ends need to be long enough to let the camera run from your hip to your face. If it is a standard camera strap it will be designed to attach to either side of the camera, and because you are creating a speed strap, you'll need a way to join the two ends together instead of attaching them to the camera strap mounts. A simple ring and buckles will do the job. This way you'll also be able to adjust the length as necessary.
Lastly, you need a bit of extra security! In case the worst happens, have an extra strap loosely connecting the camera to your body or to the strap. Why? sometimes after a lot of activity, the base plate 'may' loosen, or in my case - as mentioned above, the clip broke - and my camera ended up lens first in the dirt in the middle of a rodeo arena - doh! (I had my security strap a bit too loose). I ended up attaching an extra clip and ring to the slide ring and attached it to the camera strap mount which worked out to be the best system ever! (The extra security extra strap did get in the way a bit and I felt all tied up in extra straps when I was carrying 2 cameras with speed straps)
So there is a little fine tuning to do depending on what parts you have to build with, but it's a fun and worthwhile project! Your camera will sit by your side in a much more comfortable position, and it will be quickly available and very safely attached to you.
Start your search on eBay or Amazon - have fun!
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