The thickness of the sperm itself isn't really determined by anything. It just comes as it is. The sperm thickness can vary between the times of sexual activity such as sex and masturbation. However, it has been commonly and somewhat proven that lifestyle, diet, health, age, etc could be a factor found in sperm thickness.
Genes.
Voltage determines a cable's insulation thickness, not its conductor thickness (or, more accurately, its cross-sectional area). It's current that determines the csa of a conductor, not voltage.
You need to get a boner then rub your dick till you give sperm.
The width and thickness of the nail is determined by the size, length, and thickness of the matrix, while the shape of the fingertip itself determines if the nail plate is either flat, arched or hooked. (Matrix- is where the nail forms and is responsible for the production of the cells that become the nail.)
The length ,thickness, and alloy of the filament determines its resistance. The lower the resistance, the lower the voltage required to power it.
The sperm cell, which is a gamete.
The thickness and curliness varies by color (diameter) and by the melanin content (pigment).
The genes that are carried in the sperm to the ova. If the 23rd chromosome of the sperm is 'X', the offspring will be female. If it is 'Y', the offspring will be male.
It's not so much the thickness of the semen, but the number of sperm within the semen. Only a doctor can determine that.
1 - it determines the sex if it fertilises the ovum
Yes, they do. The gauge of a guitar string determines its thickness and therefore its pitch.
The consistency of ejaculate can vary quite a bit with hydration (how much water you drink) level and there is certainly a genetic component. The secondary question is why? The "thickness" is not a specific indicator of semen quality and, since there are several "fractions" (components) to semen, "thickness" is not necessarily an indicator of quality or sperm count.