The percentage elongation of a material as obtained from a static tension test depends upon the gauge length of the specimen.

The gauge length is the portion of the specimen over which the elongation is measured during the test. It is the distance between two reference points on the specimen, typically marked by two dots or lines. When the material is subjected to tension, it undergoes deformation and elongation. The gauge length is used to measure the elongation of the material.

Explanation:
1. Gauge Length: The gauge length is an important parameter in the static tension test. It determines the portion of the specimen that undergoes deformation and elongation. The elongation is measured by comparing the change in length of the gauge length before and after the test. The longer the gauge length, the more elongation can be measured accurately.

2. Diameter of the Test Specimen: The diameter of the test specimen does not directly affect the percentage elongation. It primarily affects other properties such as the load-bearing capacity and stress distribution. The percentage elongation is mainly influenced by the gauge length.

3. Nature of End-Grips: The nature of end-grips of the testing machine does not significantly affect the percentage elongation. The end-grips are used to hold the specimen securely during the test, but they do not directly impact the measurement of elongation. The gauge length is the key parameter that determines the elongation.

4. Geometry of the Test Specimen: The geometry of the test specimen, such as its shape and dimensions, may indirectly affect the percentage elongation. However, the gauge length is still the primary factor that determines the elongation. The geometry of the specimen primarily affects other properties such as the stress concentration and strain distribution.

In conclusion, the percentage elongation of a material as obtained from a static tension test depends mainly upon the gauge length of the specimen. The gauge length determines the portion of the specimen over which the elongation is measured. Other factors such as the diameter of the test specimen, nature of end-grips, and geometry of the specimen may have indirect effects but are not the primary determinants of elongation.