We have high quality drill bits in a number of sizes to match the hinge spindles:
The drill bits are manufactured by Nachi of Japan
For 6.35mm spindles, one can use the commonly available 1/4" drill bits
After enlarging the bore with the drill bits, in some cases, there can be some burrs or unevenness in the center part of the hinge, such that the spindle will fit tight. If the center part of the hinge is too tight, the hinges will not freely rotate. In such cases, the best way is to use a reamer to clear such burrs or unevenness, or contact us. We can share some tradesman tricks that will usually resolve the issue.