Solid PTFE; with metal band and choker spring. Stem diameter: 3/8" (0;375"); valve guide diameter: 0;562"; over all length of seal: 0;518"; outside diameter of seal: 0;650". Kibblewhite Precision Machining custom valve stem seals are a quality product and suitable for any and all custom application. Note: Below mentioned valve stem diameters are for reference only. - 36-84 B.T. = 3/8" (.3750") - 57-83 XL intake = 0.3090" - 57-83 XL exhaust = 0.3384" - 84-04 B.T.; 86-03 XL = 5/16" (.311") - 05-16 TCA/B; 04-22 XL; 08-12 XR = 7mm (.2760") - 02-17 V-Rod = 6mm (0.2345") - 17-24 M8 = 6mm (0.2345") Installation note: Valve guides made of PTFE require another fitment technique than ''regular'' or non-PTFE valve guides; this is due to the PTFE material. They are typically 0.020" (0.50mm) smaller than the valve stem and guide top they’re designed to fit. - The guide top should have a decent chamfer - The valve stem should have a decent chamfer; but a mylar seal installation protector / installation capsule (501823 green 5/16" / 0.3125"; 501824 Yellow 11/32" / 0.34375"; 501825 3/8" / 0.375") is advised for easier installation over the valve stem - You have to kind of roll the seal around the valve tip while exerting downward pressure to get it started - Don''t push directly on the very top of the seal to get it on to the guide; you’ll collapse the sealing area and tear the seal - A 12 point 12mm socket catches the shoulder of the guide pretty well and can be used to push t