easy way to fit new sight,set sight base in vice so the dovtail angle on sight base is parell with vice jaws + the height of a steel enginers ruler laid flat on jaw top of vice remove ruler and file to jaw top ,check for squar both sides should be same,turn over and repeat it now should be a very tight fit diferance in dovetail width at base is 2mm ruler thickness is 0.994mm so you should have atight fit if to tight very carfuly stone being carful to keep squar best to do this with sight bass put back in vice as before,mack sure vice jaws are smooth so it wont mark sight bass, most vices have reversable jaws and jaws are to haed for a file to cut easly but go slowly just in case,you need jas as a marker for height