Two highly satisfactory thin-section holders have been constructed and put into use. These help materially in the ease of preparing petro-graphic thin sections. The boron carbide holder used for coarse grinding has an automatic section-thickness control. This automatic control eliminates the many time-consuming inspection-correction steps during coarse grinding and assures a uniform product for finish grinding. The plastic holder used for finishing aids in handling the section on the lap. The slides are less likely to pull free when this holder is used than when the slides are hand-held. This results in less breakage. Both of these holders are inexpensive and their use does not require modification of pre-existing equipment.