I have just recieved one of these myself. The bolt that i used was a 4/40 x 3/8 (they didn't have any 1/4 bolts where i was shopping) and one nut. I put the nut on the bolt and tightened it to the head of the bolt and screw it in the hole the opposite way that the original philips screw was. The only problem that i had was the bolt was too long and hit the clip on the backside not letting the blade fully close. well in about one minute with the file of my SAK Ranger (using it like a saw not as a file) it was now a 1/4" bolt. The cost of the new thumb stud was .10$ .05 for the nut and .05 for the bolt.