Cup type .75" clutch master cylinder kit. Please note that early master cylinders used an internal piston requiring a cup type main seal on the upper end. This kit can only be used with the early cylinder. Genuine Lockheed supplied. We recommend verifying that your master cylinder bore is .75" diameter at the same time. If you wish to convert your early master cylinder to the later type with improved ring main seal, see GRK3007-KIT. For later ring type master cylinder kit, use GRK3004.