  In the previous paper the author defined an infinite order plug $(P,\varphi)$
which gives rise to infinite Fintushel-Stern's knot-surgeries. Here, we give
two 4-dimensional infinitely many exotic families $Y_n$, $Z_n$ of exotic
enlargements of the plug. The families $Y_n$, $Z_n$ have $b_2=3$, $4$ and the
boundaries are 3-manifolds with $b_1=1$, $0$ respectively. We give a plug (or
g-cork) twist $(P,\varphi_{p,q})$ producing the 2-bridge knot or link surgery
by combining the plug $(P,\varphi)$. As a further example, we describe a
4-dimensional twist $(M,\mu)$ between knot-surgeries for two mutant knots. The
twisted double concerning $(M,\mu)$ gives a candidate of exotic $\#^2S^2\times
S^2$.
