The /v/ sound is spelled with <v> or <ve>. The /Ɵ/ sound is spelled <th>.
The contrast is between a voiced labio-dental fricative and a voiceless dental and alveolar fricative. Although the sounds are similar and both are potentially problematic for many learners, the contrast is so rare that it causes few problems. Note how many of the pairs involve rare or obsolete words.
Interesting pairs include:
The mean density value is 0.8%, giving some support to the O'Connor conjecture. The list makes 22 semantic distinctions, a loading of 73%.
bevel bethel bevels bethels derv dearth dove doth grove growth groves growths halve hearth halves hearths have hath heave heath helve health rave wraith raves wraiths reeve wreath reeves wreaths rove wroth trove troth vain thane vein thane veins thanes versed thirst verso Thurso Vic thick vicar thicker vie thigh vies thighs views thews vole thole voles tholes you've youth
John Higgins, Shaftesbury, October 2010.