Japanese made Brass and titanium height  adjustable nuts,

they either have a curved or flat top and some have a shoulder as in the photo

the sizes given are the overall width and the string spacing

the flat with shoulder 42mm 36mm has a flat underside

a flat top and a flat underside to the shoulder

the curved 43mm 36mm has a flat underside and a curved top.

strat

flat base, curved top 

8mm at center, 6.5mm at ends

5mm wide,

 LP curved underside, curved shoulder 

curved top, 5mm high, 5mm wide, 42 or 43mm.