ATJ6764 Pack of 12 Belleville washers.  The washers are built up as a compression spring and should be adjusted as per these instructions;

First fitted to Nuffield 345 and Nuffield 465 tractors with depth control hydraulics then fitted to following Nuffield, Leyland and Marshall tractors.

Fitted to tractors:

• Nuffield 3/45, 4/65
• Leyland 253, 245, 344, 384, 255, 270, 262, 272, 462, 472, 282, 482, 502, 602, 604, 702, 704, 802, 804
• Leyland 285, 2100, 485, 4100
• Marshall 502, 602, 604, 702, 704, 802, 804, 902XL, 904XL
• Marshall 752XL, 754XL, 852XL, 854XL, 952XL, 954XL