The attached image is of two variations of screwless epee tips, FWF on the left and Estoc on the right. The primary differences lie in the length of the tip portion which allows the FWF tips to use an standard unmodified epee spring. Both types use a standard pressure (750 gr) spring. In my experience you have to modify a standard contact spring for the Estoc brand by cutting off 3 turns of the contact spring and then slightly crimping the end which the threaded center post is screwed into. This is a serious issue and takes a great amount of time and effort. I have obtained Estoc branded contact springs which supposedly remove the need to modify the contact spring. I have yet to see that this works. Both designs suffer in one aspect, i.e. the center post rotates. In practice this means the contact spring rotates and the area of the contact spring's end turn which touches back to itself also is rotated. So it is possible that for light touches even when the contact spring makes contact with the one of the two contacts that the other may not be in full contact, i.e. not a completed circuit. In my experience if the tip is fully depressed then a fully completed circuit usually results. However I've seen by depressing the tip and rotating it I can see momentary breaks occur and some rotational positions when combined with the phase of the moon and other influences can cause the tip to not fire, i.e. make a full contact. One weakness which I've run into with the FWF and also the Estoc is that the small plastic washer (seen as white in the photo) can become pulled off, i.e. the screw threads (made in plastic) can be stripped off. This has occured when the tip catches on something such as a guard edge or even when being pulled from a weapons bag.