A Commentary, Critical, Practical, and Explanatory on the Old and New Testaments, by Robert Jamieson, A.R. Fausset and David Brown  at sacred-texts.com
rut 3:2BY NAOMI'S INSTRUCTIONS, RUTH LIES AT BOAZ'S FEET, WHO ACKNOWLEDGES THE DUTY OF A KINSMAN. (Rut 3:1-13)
he winnoweth barley to-night in the threshing-floor--The winnowing process is performed by throwing up the grain, after being trodden down, against the wind with a shovel. The threshing-floor, which was commonly on the harvest-field, was carefully leveled with a large cylindric roller and consolidated with chalk, that weeds might not spring up, and that it might not chop with drought. The farmer usually remained all night in harvest-time on the threshing-floor, not only for the protection of his valuable grain, but for the winnowing. That operation was performed in the evening to catch the breezes which blow after the close of a hot day, and which continue for the most part of the night. This duty at so important a season the master undertakes himself; and, accordingly, in the simplicity of ancient manners, Boaz, a person of considerable wealth and high rank, laid himself down to sleep on the barn floor, at the end of the heap of barley he had been winnowing.
rut 3:4go in, and uncover his feet and lay thee down--Singular as these directions may appear to us, there was no impropriety in them, according to the simplicity of rural manners in Beth-lehem. In ordinary circumstances these would have seemed indecorous to the world; but in the case of Ruth, it was a method, doubtless conformable to prevailing usage, of reminding Boaz of the duty which devolved on him as the kinsman of her deceased husband. Boaz probably slept upon a mat or skin; Ruth lay crosswise at his feet--a position in which Eastern servants frequently sleep in the same chamber or tent with their master; and if they want a covering, custom allows them that benefit from part of the covering on their master's bed. Resting, as the Orientals do at night, in the same clothes they wear during the day, there was no indelicacy in a stranger, or even a woman, putting the extremity of this cover over her.
rut 3:9I am Ruth thine handmaid: spread therefore thy skirt over thine handmaid; for thou art a near kinsman--She had already drawn part of the mantle over her; and she asked him now to do it, that the act might become his own. To spread a skirt over one is, in the East, a symbolical action denoting protection. To this day in many parts of the East, to say of anyone that he put his skirt over a woman, is synonymous with saying that he married her; and at all the marriages of the modern Jews and Hindus, one part of the ceremony is for the bridegroom to put a silken or cotton cloak around his bride.
rut 3:15Bring the veil that thou hast upon thee, and hold it--Eastern veils are large sheets--those of ladies being of red silk; but the poorer or common class of women wear them of blue, or blue and white striped linen or cotton. They are wrapped round the head, so as to conceal the whole face except one eye.
rut 3:17six measures of barley--Hebrew, "six seahs," a seah contained about two gallons and a half, six of which must have been rather a heavy load for a woman.