[6] On July 19, 1937, he defeated Ruby Bradley, a well known opponent, at Arena stadium in Philadelphia in a fourth-round technical knockout.

Jeffra captured the World Bantamweight title at age 23 by outpointing Puerto Rican great Sixto Escobar on September 23, 1937 in a fifteen-round points decision in New York's Polo Grounds.

[8] Jeffra, however, lost the title to Escobar in his home country in San Juan, Puerto, Rico, on February 20, 1938 in another classic fifteen round points decision before a crowd of around 13,000.

[9] At least one source considered the restrictive dieting and heavy work outs required by Jeffra to make the 118 bantamweight limit, and the resulting lack of stamina, to be one of the causes of his loss to Escobar.

On May 20, 1940, Jeffra outpointed Archibald to win the NYSAC (New York) version of the World Featherweight Championship in a fifteen rounds unanimous decision in his hometown of Baltimore.

Though Archibald attempted comebacks in the eighth and ninth rounds with a strong showing, it was not enough to affect Jeffra's wide margin.

[11] On July 29, 1940, he successfully defended his NYSAC World Featherweight Title against Spider Armstrong in a fifteen-round Unanimous Decision at Carlin's Park in Baltimore.

In their third meeting on February 2, 1942, he beat Speary in a ten-round Split Decision before a crowd of 7,000 at the Maple Leaf Gardens in Toronto, Canada.

On September 8, 1941, he defeated well known boxer Tommy Forte in a ten-round unanimous decision at Shibe Park, in Philadelphia, Pennsylvania.

[1] On November 10, 1941, Jeffra again defeated great rival Joey Archibald gaining a ten-round Unanimous Decision in Providence, Rhode Island, taking the lead early and never losing it.

[14] Jeffra lost a NYSAC World Featherweight Title bout to reigning champion Chalky Wright on June 19, 1942, before a crowd of 6,000 at Oriole Park in Baltimore, in a ten-round technical knockout.

[15] On March 27, 1944, Jeffra fought an important non-title bout with former NBA World Bantamweight Champion Lou Salica, winning in a ten-round unanimous decision in his hometown of Baltimore.

[16] On November 20, 1944, Jeffra scratched out an important but close victory in a non-title bout against former NBA World Featherweight Champion Phil Terranova in a ten-round split decision in Baltimore.

[17] Jeffra defeated such men as Lou Salica, "Pittsburgh" Jackie Wilson, Ruby Bradley, Joey Iannotti, Indian Quintana, and Bill Speary.