Before cutting a bolt down thread two nuts onto it, lock them together with two spanners ideally at exact point you want to cut the bolt's thread. Then cut the bolt and remove the nuts. They will remove the burr in the thread and your bolt should be correct length and thread in smoothly.
PARTS FOR SALE:
vintage Brooks Professional saddle | Specialized FACT CX fork | Columbus fork | Reynolds 531 fork | Avid Arch Rival v-brakes | various 700c, 27" and 26" wheels | vintage Weco hubs (fixed/freewheel) | vintage Raleigh ladies frames + lots more!