Perhaps this sounds like a trivial question, but I don't understand how a maester can wear a chain when it is formed of just one link; even five links would surely not be enough to fit around a man's neck. Do they not wear the chain until it can physically be worn? Do they tie string from the front chain to the back chain?
From the Wiki of Ice & Fire:
A student-maester with a link is known as an acolyte until he has a full chain; The student-maesters do not wear the chain until it is full; it is not until he has completed extensive study in various subjects and has earned enough links to form a chain (to be worn around the neck) that he is considered worthy of advancement to the title of Maester, no longer a student but a peer.
They have to earn quite a few links to form a full chain before they can wear it, and be considered full Maesters.
Maesters wear a chain around their necks composed of various substances to signify their personal expertise. Each link indicates a different field of study. There are hundreds of recognized fields each with a different representative substance. Maesters are expected to wear their chains at all times, even when sleeping.
While there were seven known metals used, several fields shared their metals with others. One didn't became a maester without studying and mastering scores of fields first thus even a novice maester has a chain of considerable length.
They wear their links on a leather thong around their necks.
Armen [the Acolyte] wore a leather thong about his neck, strung with links of pewter, tin, lead and copper...
A Feast for Crows, Prologue
One can assume that they remove the leather thong when they have enough links for the chain to fit around their neck.
It appears as though the novices and acolytes do not wear their chains until they become a maester at which point it should be long enough to be worn. Note that I am only interpreting this from reading between the lines of the following quotes as nothing seems to be mentioned explicitly.
Alleras would make a maester. He had only been at the Citadel for a year, yet already he had forged three links of his maester's chain. Armen might have more, but each of his had taken him a year to earn. Still, he would make a maester too. Roone and Mollander remained pink-necked novices, but Roone was very young and Mollander preferred drinking to reading.
A Feast for Crows, Prologue
And so I did. I forged the first link in my chain at three-and-ten, and other links followed. I completed my chain and took my oaths in the ninth year of the reign of King Robert, the First of His Name, and found myself blessed to continue at the Citadel, to serve the archmaesters and aid them in all that they did.
The World of Ice and Fire, Preface
Note though that Maester Luwin is said to have his chain quite tight around his neck, the same goes for some others.
Luwin slid a finger up under his collar and began to turn it, inch by inch. He had a thick neck for a small man, and the chain was tight, but a few pulls had it all the way around. "This is Valyrian steel," he said when the link of dark grey metal lay against the apple of his throat.
A Clash of Kings, Bran IV