C lose bounds are obtained to the plastic constraint factor for any symmetrically V-notched tension bar of rigid/plastic material under conditions of plane strain. The estimated factors are well represented by 1 + In {(ω + 1)/2} or 1 + 1 2 π-α, whichever is the lesser, where 2α is the notch angle and ω is the ratio of bar width to root width. When these expressions are equal the geometry is critical in the sense that for smaller ω or α the plastic flow is not localized around the root section.