Tetrahydrofuran (THF), widely used as a mobile phase for GPC, attacks the CTFE valve stems and TFE/propylene o-rings used in the standard Five Valve Cap. This special THF-resistant version has 316 stainless steel wherever the standard system has CTFE, and Kalrez® o-rings in place of the TFE/propylene o-rings. This cap is also recommended for aggressive organic solutions such as chlorinated hydro-carbons, ethers, and ketones. Cap body is manufactured from glass-filled PTFE. Cap will fit any reservoir or bottle with a GL 45 thread. Patent No. 5,397,467.