Importance

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Abstract

Three collar groups 6A through 6C, each group comprising collars 5a through 5b, 5c through 5e and 5f through 5h which are thin walled and close to each other are provided in a spaced manner in a piston sliding direction. A first group 6A which is provided at the front most end of the piston head 5 comprises two collars 5a and 5b. The front collar 5a which is in contact with the liquid drug has a larger diameter than that of the rear collar 5b. First and third collar groups 6B and 6C which are at the rear of the first collar group 6A comprise three collars 5c to 5e and 5f to 5h, respectively. The intermediate collars 5d and 5g have larger diameters than those of the front and rear collars 5c and 5e; and 5f and 5h, respectively. A support collar 5i is provided at the rear of the collar groups 6B and 6C in such a manner that it is spaced therefrom. The support collar 5i has a thick walled portion x at its base excepting the peripheral edge thereof.

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First Claim